By manipulating the flow of nature itself, large dams provide enough power to light up entire cities, but power comes with a price.

Experts say dams disrupt the flow of the rivers they occupy, which can negatively affect everything in the water.

âÄúDams are almost always tremendously damaging to ecological systems,âÄù said Pat Nunnally, coordinator for the Institute on the EnvironmentâÄôs River Life program. âÄúThe whole way the river works is fundamentally changed.âÄù

River Life hosted a two-day event this week to talk specifically about what kind of damage dams cause, and what can be done to solve the problem.

Gordon Grant, one of the eventâÄôs speakers, said that there are two negative consequences of dams that seriously harm ecosystems.

âÄúVirtually all dams block the migration of fish,âÄù said Grant, a research hydrologist with the U.S. department of agricultureâÄôs forest service. There are several strategies that can be employed to help fish continue on their seasonal journeys, but all are very expensive.

Dams also block the flow of sediments that sometimes contain harmful chemicals.

âÄúYou may have 40, 50, 60 years of agricultural chemicals that may have come down and accumulated in the sediments,âÄù Grant said.

Historically, dams have also been known to flood large areas of land. MinnesotaâÄôs early Native population felt the effects of dams first hand centuries ago when the federal government in the northern portion of the state built dams.

âÄúThe impact for Native communities in northern Minnesota was devastating,âÄù said Anton Treuer, professor of Ojibwe language at Bemidji State University, and one of the eventâÄôs speakers.

âÄúWildlife was flooded out, cranberries were flooded out, communities were flooded out,âÄù he said. âÄúThe rice crops and the cranberry crops have really never recovered.âÄù

Several strategies to curb the negative effects of dams have emerged since that time. One solution to disrupted fish migration is to build a fish ladder âÄî a lined concrete channel with small steps that fish can navigate over or around the dam. But even fish ladders, which are expensive to build, do not always solve the problem, Grant said.

Another solution is to remove the dams altogether.

âÄúDam removal has immerged as one of the strategies, but you have to be careful,âÄù Grant said.

Dam removal has become a frequent process in the western half of the Unites States. Usually small dams are removed, where there is not a large amount of sediment stored behind it, Nunnally said.

âÄúItâÄôs tricky. Getting rid of a dam is tricky,âÄù Grant said.  Because dams do not all behave equally on rivers, removing one dam may have a different effect than removing another, he said.

If a dam that has a large amount of sediment stored behind it is removed, the sediment may suddenly rush down the river, causing further harm to ecosystems, Grant said.

Nunnaly said he hopes conversations about dams and their effects will continue in the future and real solutions will be proposed.

âÄúNothingâÄôs simple,âÄù Grant said. âÄúA dam is not a dam is not a dam âĦ you just canâÄôt paint them all the same color.âÄù