The truth behind hydropower plants

About 16,4% of worlds electric energy was produced by hydropower plants in 2016 and the percent is still rising due to more and more of them being built every year. It is stated, that they:

  1.    Are environmental friendly,

  2.    Provide clean energy that is completely renewable and sustainable,

  3.    Help maintain farming lands (accumulation of water that can be used for watering the fields        in time of need)

  4.    Provide fishing areas.

Don’t get me wrong, to some extension all of these statements are true,
but there is more going on than you know.

1. Are environmental friendly

Hydropower plants are environmentally friendly since they don’t produce waste or release carbon or other gases. The only change in the environment that we see is the power plant itself, a slightly different shape of the river and, of course, some missing trees. On many hydropower plants, there are also fish passes, that help fish migrate and sustain the populations! So where are the downsides here?

First, we need to know, that with building the dam, we change much more than just the looks of the river. With this, we reduce the speed of the water flow which is the first step leading to strongly changed conditions. In the accumulation, the water temperature starts to rise, which is followed by changes in oxygen levels, pH levels, etc. Because of the built wall, sediment can’t pass freely and is being loaded (together with heavy metals and other polluters) behind the wall. In time, the spaces between larger sediment particles (so-called interstitial spaces) fill with smaller sediment particles. With this step, many aquatic invertebrates (fish food) lose their homes and so food becomes more scarce. This, together with low oxygen values, low current speeds, and many other changed factors, lead to species migrations (potential loss of keystone species or ecosystem engineers) and overall changes in community composition.

Related articles:

What are keystone species?

What are ecosystem engineers? 

Fish passes only need to be built on streams and rivers, where migratory fish are present and they need to follow some regulations. The problem with this idea is, that every fish has its own biology and therefore different requirements in order to actually use the fish pass. In general, fish are divided into two groups Salmonidae (that require high current speeds) and Cyprinidae (that require low current speeds). Old fish passes are usually suitable only for one of the listed groups, while the ones constructed now, usually have a high diversity of current speeds. Here is a picture of one small power plant (that probably isn’t used to produce electricity) but still acts as a barrier on the stream. 

2. Provide clean energy that is completely renewable and sustainable

The energy produced in this way is completely clean since we are not using fossil fuels (coal, natural gas, and oil), so there are no CO2 emissions. It is only water, flowing in a bit different way, being led through a turbine. Hydropower is also one of the sustainable energies available and it presented about 85% of all renewable energy produced in 2016. Water will flow forever (if we don’t dry out the river) so it really is a great, sustainable and renewable source!


Yes, the fact that it has no emissions and that they are not using any fossil fuels is true but it is also true for all other green energies (solar, wind, geothermal, ocean current etc.). We have already talked about the changes that happen when we build a dam, but there is one other, critical part of the power plant – the turbine. Since this is the more or less the only moving part of the power plant, it is mostly responsible for injuries of the organisms (mostly fish) trying to pass it.

Related article: Obtaining energy from wind turbines

How successful the organisms are in passing, is largely dependent on their biology as well as the speed of the turbine, its position, and its design. Scientists are putting a lot of effort in designing innovative hydropower plants, that would have a lower impact on the environment and organisms trying to pass it. Until now they have managed to reduce the damage done to the fish, but there is still a long way to go, to make them completely fish and environmentally friendly.

fishes-water-turbine-2When it comes to hydropower, people are mostly talking about its sustainability. It is true, that the water flow is an ongoing source, but everything else is not. In other words: when we build a dam, the only thing that is sustainably changed is the river and its processes. Even if we would demolish the dam, many of the processes would need a long time to re-establish. The biggest problem of all would probably be presented by sediment (together with all the heavy metals and polluters). When the barrier would be removed everything, that was accumulating behind it would start to allocate downstream.

This would affect many habitats and organisms on its way since they wouldn’t be adapted to these new, higher levels of present substances. Many changes in community structures inside the river would need to be made as well as in tightly connected ecosystems. When concentrations of substances would (in time) come back to the levels they were before, communities would re-establish too.

3. Help maintain farming lands

With water accumulations, gathering the needed water for watering the fields is not such a big problem anymore. In events of droughts, there is always some water present in them that can be used. If too much water is applied it runs back to the accumulation, where it can be used again, so we are actually recycling the water and we only use as much as we really need!

In cases of bigger droughts, we should first check, if there is any water left in the stream under the dam. As we all know, fishes (and other water organisms) can’t live on land. They also can’t survive for long in little, disconnected puddles. If you see any of these cases, unfortunately, these organisms are as good as dead. The minimal water depth is usually defined by the responsible organization and can vary between the countries.

The water (either pumped from the accumulation or rainwater) that goes through the field and is being returned to the river represents a big ecological problem. The reason for this is, that many fields are treated with fertilizers or pesticides and when water is applied, the substances are being dissolved and carried to the river. Pesticides and fertilizers can present a direct health hazard if they are not stored or used by plants. Effects of high concentrations of fertilizers in the river are best seen in accumulations where algae are present in high densities. There are two major problems with this phenomena. The first one is the production of toxins, that are toxic to all live organisms including people. The second problem is, that when algae consume most of the nutrients, they start to die and decompose. The process of decomposition uses a lot of oxygen, leaving only a little or none left for other organisms. This can result in migrations (if possible) or death of these organisms.  

4. Provide fishing areas

These accumulations provide perfect fishing grounds. There are many fish present on both sides of the wall, creating a real paradise for fishermen!

Well, yes, of course, the density of fish on both sides of the barrier is higher. The fish (no matter where they are) are facing a barrier. The ones, living on the upper part need to somehow pass the predators when migrating downstream. The ones that are living in the lower part first need to find the fish pass and then be able to use it. 

Another thing we need to talk about is how healthy these fish are for consumption. Ones, that are living in accumulations usually have high concentrations of polluters and heavy metals stored in their tissues. This is because of a process called biomagnification, with which we describe transportation of stable substances up the food chain. Because of this process, higher concentrations of problematic substances are found in organisms on top of the food chain and older organisms. younger organisms and the ones at the bottom of the food chain contain lower concentrations. It is safe to say, that none of the fish found in this kind of accumulations are an example of a healthy fish, because also for them: you are what you eat, applies.

6 thoughts on “The truth behind hydropower plants

  • I had no idea how these “little things” like just building a dam could actually be an ecological risk…
    Good to know what we don’t know, I guess.
    Interesting writing, by the way.

  • So would you say continuing to work on the engineering behind hydropower plants would be the next step/best alternative? Biomagnification and the low oxygen levels absolutely create an issue with water life. This reminds me of the points made in Patagonia’s documentary DamNation. Great article!

    • I would say that there are two possible alternatives. One is what you have suggested – researching new options to make the engineering better and the other is to research completely new possibilities (by this I also mean other options of obtaining energy). The documentary film you mentioned is really worth seeing and gives a good overview of the topics. Thank you for stopping by!

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