CHICAGO (CBS) – The Illinois Environmental Protection Agency has allowed state power generators to increase the temperature of cooling water that can be discharged into lakes and rivers, because of this summer’s heat and drought, but an environmental group says that might not be a good idea.

Josh Mogerman, with the National Resources Defense Council, said the heat wave warmed up intake water for power plants, and reduced the amount of water available to cool their equipment.

“They’re running at higher temperatures because the water that is being brought in to cool the facilities has been heated by our hot weather. It’s also an issue of – in some cases – not being able to get nearly as much water, because of the drought,” Mogerman said.

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That led to the Illinois EPA and the U.S. Nuclear Regulatory Commission allowing power plants to dump hundreds of millions of gallons of water at much warmer temperatures than normal.

The NRDC says the warmer water being dumped by power plants – at temperatures approaching 100 degrees – can kill fish in the state’s lakes and rivers, or drive them deeper into the water and out of their natural habitats to cool off.

“That impacts fish that are evolved to live in a specific sort of a temperature. You’re basically scalding the fish; forcing them either to dive deeper for cold water, or in the case of our rivers, we’re boiling them,” Mogerman said.

Mogerman suggested another solution to the problem of power plants having to use warmer water to cool their equipment.

“In the state of Illinois, we have an excess of electricity generated, so we do need to be looking at whether these facilities need to be operating at peak level, or whether we can deal with some of these other threats by throttling back,” Mogerman said.

Utilities said the power was needed for air conditioning during the summer’s heat wave.

Mogerman said the issue is larger than one hot summer.

“We shouldn’t be thinking about our power plants in the context of just one year’s drought, or one year’s heat wave. It’s very likely that the condition’s we’re seeing are going to become more normal,” Mogerman said.

He suggested power plants instead should cut back on electricity generation, since Illinois has a power surplus, and update their equipment to be more heat-efficient and reduce carbon dioxide emissions.

“Ensuring that we have a modernization of our – in some cases – outdated electrical generation fleet, to deal with these issues,” he said.

Power companies have said producing less power would have meant less air conditioning for customers, hardly a viable option during this summer’s record heat.