With a heat wave warming the Mississippi River water used for cooling at the nuclear power plant in Quad Cities, Illinois, Exelon Corp. has cut the power at the plant about 19 percent, a spokeswoman said on Tuesday.

The 867-megawatt Quad Cities reactors were producing about 700 megawatts of power each after the reduction. The plant uses river water to condense steam from the turbine before returning the condensed water back to the reactor, while the river water flows back to the river.

With temperatures exceeding 90 degrees in the area around the plant, the hot river water can harm fish and other aquatic life and does not cool the reactor water as efficiently.

Meteorologists forecast temperatures in the area around the plant would reach 93 degrees Fahrenheit, according to forecaster AccuWeather.

This week, nuclear operators have reduced power output at several reactors due to high water temperatures including Xcel Energy Inc.'s Prairie Island 1 and 2, and Monticello units in Minnesota over the weekend, and Exelon's Dresden 2 unit in Illinois on Monday.

The 1,734 MW Quad Cities station is in Cordova in Rock Island County, about 155 miles west of Chicago. There are two 867-MW units, 1 and 2, at the station. Each entered service in 1972.

One MW usually powers about 800 homes but during a heat wave a megawatt powers fewer homes.

Exelon's unregulated Exelon Generation Co LLC subsidiary operates the station for its owners, Exelon (75 percent) and Berkshire Hathaway Inc.'s MidAmerican Energy Co. subsidiary (25 percent).

Exelon owns and operates more than 38,000 MW of generating capacity, markets energy commodities, and transmits and distributes electricity (5.2 million) and natural gas (460,000) to customers in Illinois and Pennsylvania.

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