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Updated: May 19, 2022


I’ve been fortunate to travel and see amazing rivers, waterfalls and lakes. Yosemite has amazing waterfalls such as Bridal Veil, Upper and Lower Yosemite Falls. Alaska has beautiful wide rivers like Matanuska. It is such a privilege to see water flowing unimpeded and clean.

I hike a lot in New Hampshire and often view the streams coming down through the woods. It looks so natural. The streams blend with the trees, the ground, the rocks and the bugs and wildlife around the water.

I thought a lot about dams over the years. I think about the man-made dams rather than the dams made by beavers which may also have their problems but they have environmental benefits as well. The Hoover Dam and multiple dams in northwest come to mind. I think about the questions. “Who's water, is it?” What gives somebody the right to dam up in one location and restrict the flow somewhere else? How do fish pass? If the dam is for power, could part of a river be blocked instead of the whole thing? Can a canal be built diverting part of the flow? Have you ever canoed or kayaked a river and realized that there would be multiple locations where you would have to take out to avoid a dam? Does a dam stay productive? Do dams require maintenance? What happens to the temperature of the water? Do the rivers become tame instead of naturally wild? Does water get redistributed to other areas for irrigation? Can part of a river be dammed instead of the whole thing?

Some of the problems with dams include water stagnation, warming of water, buildup of sediment, lower dissolved oxygen levels, blocking the movement of fish, displacing towns and natural areas, slowing rivers that should run quickly, separating fish from accessing there former starting or finishing points, disrupting habitat for other animals, and changing delta system of major rivers. Also, there are financial costs to maintaining them. There is the cost and sometimes devastation if dams fail or aren’t big enough to handle severe storms. They may encourage settlement of people where otherwise they should not be settled.


I grew up in Massachusetts. When I could walk and explore the woods around our dead-end street, I would sometimes head to Box Pond on the Charles River. I could see catfish in there and turtles. It is dammed at Depot St and Box Pond Road. The dam interesting cool but not natural. I remember seeing trash and foam at the bottle of the dam on the downflow side.

The state of Massachusetts explains “Massachusetts has more than 3000 dams.” “Most dams in Massachusetts were built in the 1700s and 1800s to power small mills. These dams have outlived their original purpose and are aging. Many dam owners choose to remove their dams in order to reduce their liability and eliminate the long-term cost of inspections and repairs.” “Since 2005, The Division of Ecological Restoration (DER) has removed over 40 dams.” Fortunately, per “between 2000 and 2018, 60 dams were removed in Massachusetts, and more are being removed every year.”


Clean hydro-electric power from dams has been one of the great benefits of dams. However, it has not been without consequences. If dams are removed or are less effective, that power will have to be made up from others sources.

To illustrate the scale of the problem, the ten largest dams in the world are illustrated below.

“The Kariba Dam, Zimbabwe is the world’s biggest dam based on water storage capacity. It generates 1,470MW of energy.”

“The Bratsk Dam in Siberia, Russia, ranks as the second biggest dam in the world.” The dam can generate 4,500MW of power.”

“Akosombo dam, located in Ghana, is the third biggest dam based on water storage capacity.” It can generator 768,000kw of power.

“The Daniel Johnson Dam, also known as Manic 5 Dam, in Quebec” It has a capacity of 2,660MW.

“Guri in Venezuela, the world’s fifth biggest dam, has a storage capacity of 135 billion cubic metres.” It has an installed capacity of more than 10,000MW.”

“The Aswan High Dam, which impounds the River Nile is the sixth biggest dam based on water storage capacity.” It has capacity for 2,100MW.

“W.A.C Bennett Dam, constructed on the Peace River in British Columbia, Canada, creates the Williston Lake. The dam ranks as the seventh largest with a storage capacity of approximately 74 billion cubic metres and covers a surface area of 1,773km2.“ It can generate 2,790MW.“

“Krasnoyarsk Dam in Russia is the world’s eighth biggest dam is the.“ It has capacity of 6,000MW.

“The Zeya Dam, built on the Zeya River in the Amur Oblast of Russia, is the ninth biggest dam based on reservoir capacity.” It can generate 1,290MW.“

“The Robert Bourassa Dam impounding the La Grande River in northern Quebec, Canada,” It has a capacity of 5,616MW.

These are just the largest. There are thousands of other dams around the world. The Sierra Club states that “hydropower is considered a form of clean energy by some because it does not rely on fossil fuels. However large hydropower projects entail significant costs both ecologically and in terms of environmental justice.” Wind and photovoltaic should be looked at as renewable alternatives.


Dams can create water storage, control floods, provide for irrigation and provide for recreation. They can also fail. They can only hold back so much capacity. Dam designs may be too old to take into consideration the storms created by climate change. And, water for irrigation may be solving one problem and creating others.

This year, 2022, Lake Mead and Lake Powell, both on the Colorado River, are at historic lows due to the current megadrought. The level was so low that it exposed a body in a barrel at the bottom of the Lake Mead. And, authorities are holding back water in Lake Powell to avoid shutting down the power capability of the dam. The lakes provide water to California, Nevada, and Arizona.

Hetch Hetchy Dam in Yosemite on the Tuolumne River serves San Francisco with water and power. It submerged a valley that is said to be a grand valley such as the famed Yosemite Valley floor near El Capitan and Half Dome.

Locally, the Windsor Dam forms the Quabbin Reservoir in Massachusetts. It is one of the water sources for Boston. The dam submerged four towns and about 60 hills and mountains.

There are multiple reservoirs in Texas including White Rock Reservoir where I lived briefly in 2012 and 2013. It was created by the White Rock Dam flooding the farms of two families.”

These are just examples that are repeated around the world. Reservoirs created with a lot of unintended consequences. It’s ironic that reservoirs from dams that are often designed to create flood control are used to flood the upstream side of that damn.


Dams are destructive to wildlife habitat. They interrupt flow, change salt marshes and tidal marshes, increase likelihood of invasive species, create barriers to fish breeding and spawning, reduce food stock for whales and birds and other wildlife, and submerge entire habitats upstream.

Per Massachusetts, “elevated stream temperatures and low dissolved oxygen levels associated with small dams can result in increased stress and death to fish, mussels, stream insects, and other aquatic organisms. As streams warm, native cold-water species can be replaced by non-native generalist species. “Eastern brook trout are especially susceptible to warming impacts by small dams.” And, “native shellfish, amphibians, waterfowl and plants” that “also depend on the ebb and flow of rivers,” are impacted by dams and other barriers.

Per National Oceanic and Atmospheric Association, “most salmon are adapted to living in rivers so changing their habitat to a lake often has negative consequences on their life cycle. This is especially true for activities such as spawning.”

“The presence of the dam may also change the way predators and prey interact.” “Fish delayed while trying to pass a dam are often the targets of predators. Changes to habitat may benefit predator species allowing them to increase their numbers. For example, the northern pikeminnow, a native predator [fish], prefers slow water habitat.”

“In the Columbia River’s natural state, this type of habitat was relatively rare. Now, there are many reservoirs and much more slow water habitat for the northern pikeminnow so there are many more pikeminnow to eat juvenile salmon. Changes to habitat may also allow non-native species to invade” and “compete with or prey upon native species.” There is a bounty for the pikeminnow now that is meant to help the Salmon population.

“Substrate (including sand, gravel and rocks) and large pieces of wood get trapped in the reservoir behind the dam, whereas downstream of the dam they continue to be carried away. The river below the dam may lose spawning gravel and without large pieces of wood to help form pools, the stream channel becomes straight and ditch-like. This means there is less habitat available for juvenile and adult salmon that use these substrates and pools.”

“Dams, culverts, irrigation diversion channels and other barriers restrict the ability of migratory fish species like salmon, steelhead, shad and many others to reach their historic spawning grounds. Dams “can impair and destroy these seasonal rhythms.” They “trap fertilizer and other contaminant run-off, leading to algae blooms and fish die-offs, and alter the ecology of rivers downstream.”

Dams have impacted the killer whales in the northwest of the US by decreasing Salmon that would have made it to the Puget Sound. To help start to reverse this, in the Pacific Northwest, the U.S. Fish and Wildlife Service and National Park Service played a key role in the largest dam removal and ecosystem restoration project in history, when the Elwha Dam and Glines Canyon Dam on the Elwha River were removed. This has given endangered salmon, trout and other fish access to more than 70 river miles of their historic migration and spawning habitat. This in turn helps the whales.

“In the northwest, most rivers have peak flows in the spring and lower flows in summer. The way dams use water often results in changes to these natural patterns. Reductions in peak flows may inhibit the formation of pools and riffles and other habitat types that are important to fish.”

“If dams suddenly release water or reduce flows causing river levels below the dam to rise or fall suddenly, this could strand fish.”

“Dams, dikes, roads, undersized culverts and other barriers can block tidal waters from flushing estuaries and salt marshes. The absence of natural tidal flows can cause degradation of salt marshes and estuarine habitats. Tidal restrictions can also inhibit salt marsh migration with rising sea levels. Invasive species like phragmites [a reed grass] can invade tidally restricted estuaries. Restoration of estuaries through removal of barriers and restoration of native plants and shellfish beds can help improve the environment for humans and wildlife alike.”


Dams have impeded the natural flow, increased water temperature, increased sediment, decreased nutrients going downstream, submerged towns and natural vegetation and had other negative environmental impacts.

“When dams trap sediment behind them. The sediment which might help to create or maintain a delta does not make and may cause them to reduce in size. The deltas are important for wildlife habitat.”

Per, “Small dams have a large impact on water quality.” “From 2014 to 2016, DER-supported scientists found that “dam impoundments consistently had lower water quality compared to their upstream and downstream waters.” “Negative effects from dam impoundments continue downstream.”

“Dams and their impoundments had the most negative impact on the water quality of high-gradient, cold-water streams in small watersheds.”

“All aquatic organisms require oxygen to survive. Hypoxic and anoxic zones that can form in dam impoundments are inhospitable to aquatic species. Very low oxygen levels can also reduce leaf litter breakdown and change nutrient cycling in streams, which may alter energy availability to aquatic organisms.”

“Falling water, such as from a dam spillway, may mix nitrogen from the atmosphere into the water. Water can only hold a certain amount of nitrogen, when this is exceeded, bubbles form. These bubbles can also form inside the bodies of fish which are swimming in the water causing injury or death.”

“Sediment settles out in reservoirs behind dams. Many toxic substances may be trapped in these sediments such as pesticides, or heavy metals from mine tailings. If these sediments are disturbed, these substances may be released into the water.”

“Reservoirs often produce large amounts of algae and other plants. The result is higher levels of nutrients in the river downstream” – called eutrophication “Too many nutrients can cause problems such as low oxygen levels or excessive growth of algae.”

Dams also have affected people, the Sierra Club points out that dams have had a significant impact on native Americans by flooding their land and disrupting their livelihoods with the creation of dams. That gets back to own of my questions in the introduction. “Whose water, is it?” And, the environmental costs are high. “Damming a river entails the submersion of organic material. This decomposing organic material releases methane, which is a potent greenhouse gas, much more powerful than carbon dioxide.” “There is also evidence that large dam impoundments, especially in the tropics, emit significant amounts of methane and CO2.”


Along with the cost to wildlife, landscape, water quality, erosion, and pollution, the financial costs have been enormous. There has been the cost of material, human cost of labor, and lives during construction. People have needed to be displaced. Dams that have been sold as protectors of people have been responsible for killing people instead during construction, when they have failed, or have been insufficient. For example, officially, 96 lives were lost during the construction of the Hoover Dam. When dams age, they need maintenance. When dams become obsolete, they need to be removed.

In 1928, 2500 mostly black lives were lost to a dam breach at Lake Okeechobee in Florida when a hurricane struck. With wind and water pounding the muck-wall dam, the dam failed.

Per CNN, the building of the Three Gorges Dam in China, in 1994, has resulted in “more than 158 people dying or gone missing, 3.67 million residents have been displaced and 54.8 million people have been affected, causing a devastating 144 billion yuan ($20.5 billion) in economic losses.”

The Department of Interior states, “The cost of repairing and maintaining obsolete structures can be significant – often more expensive than dam removal itself – and the cost will only grow as our infrastructure continues to age. By 2030, up to 80 percent of our nation’s dams will be over 50 years old.

Some good news, The Department of Interior states, “Over the past 20 years, the U.S. Fish and Wildlife Service has worked with 700 partners in local communities that have placed a value on free-flowing rivers to remove more than 1,638 barriers to fish passage. These projects have reopened a total of nearly 24,000 river miles, and reconnected nearly 170,000 wetland acres – benefiting over 90 native fish species and hundreds other aquatic species, birds and mammals. In turn, these improvements have supported more than 219,000 jobs in the recreation and tourism industries, generating an estimated $11 billion in economic value to local communities. These efforts join the many others that the Environmental Protection Agency, National Park Service, Bureau of Reclamation, Natural Resources Conservation Service and U.S. Army Corps of Engineers have supported across the country.“

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