Hydroelectric projects also cause an increase in mercury levels specifically methylmercury. You'd think hydroelectric would be a safe method of generating power with flooding being the only bad effect. An Inuk guy in Labrador I follow on Twitter (@AndersenAngus) is trying to raise awareness about methylmercury due to flooding of land for hydroelectric dams.
"Microbes convert naturally occurring mercury in soils into potent methylmercury when land is flooded, such as when dams are built for hydroelectric projects. The methylmercury moves into the water and animals, magnifying as it moves up the food chain. This makes the toxin especially dangerous for indigenous communities living near hydroelectric projects because they tend to have diets rich in local fish, birds and marine mammals such as seals. "
We are just so bad grasping the entire chain of effects of our actions, and the environment is incredibly complex. We need massive automated testing of environmental impact; systems that surveil ground, air, biodiversity over time all around the globe and particularly near projects like dams. It's no longer possible to just shrug it off, hope the planet can tolerate it and subconsciously accept some human loss in the name of progress.
Here is some info on it via the Harvard School of Engineering and Applied Sciences: https://www.seas.harvard.edu/news/2016/11/human-health-risks...
"Microbes convert naturally occurring mercury in soils into potent methylmercury when land is flooded, such as when dams are built for hydroelectric projects. The methylmercury moves into the water and animals, magnifying as it moves up the food chain. This makes the toxin especially dangerous for indigenous communities living near hydroelectric projects because they tend to have diets rich in local fish, birds and marine mammals such as seals. "