Iowa Lakes

ISU lake scientist John Downing said the conditions, caused in part by fertilizers finding their way into the lakes, feed algae blooms and affect the quality of the water in lakes. When the algae die, they suck up oxygen, which can kill fish and create high bacteria levels.

The lake in the best shape biologically and chemically is in Yellow Smoke Park in Crawford County, according to the latest report.

George Wyth Lake ranked ninth overall for water quality, and better than 94 percent of all Iowa lakes. South Prairie Lake in Cedar Falls ranked 11th, better than 92 percent of Iowa lakes.

Downing and colleagues from ISU and Simpson College lead teams of Iowa college students who sample and analyze water from the 132 major recreational lakes in the state.

They post the results on an Internet site that tells readers if a lake has trouble with bacteria, algae-produced toxins, cloudy water, fertilizer runoff or runaway algae. It provides the basic readings for those who really like to dig in.

The work also helps the Department of Natural Resources decide which lakes are worth restoring. In the past few decades, the department has restored 10 lakes, including the popular Lake Ahquabi near Indianola.

"The state has some tremendous assets that aren't being cared for very well," said state fisheries worker Don Bonneau. "Some lakes went down the tubes because we didn't have the money to fix them."

ISU ranked the lakes by percentile, 1 through 100. In this case, low numbers mean a lake is in worse condition or is one that's a good candidate for a restoration project. For example, a ranking of "5" would mean that the lake is among the 5 percent of lakes in the worst condition and that 95 percent of the other lakes were better off.

The Web site uses simple color coding to give the casual reader a quick idea of lake quality: red for the worst third, yellow for the middle, green for the best.

George Wyth Lake scored in the middle of the pack, at the 49th percentile, for water quality, but scored in the 92nd percentile for nutrients, indicating it doesn't suffer much from agricultural runofff.

South Prairie Lake ranked in the 71st percentile for water quality and 84th percentile for nutrients.

West Okoboji Lake, one of the state's most popular recreation spots, ranked among the top 11 percent but didn't fare as well as Big Spirit Lake, which topped 95 percent of the other lakes.

Brushy Creek Lake, popular with fishing enthusiasts, was better than 98 percent of the other lakes. Three Mile Lake in Union County was among the four best lakes.

Clear Lake, a popular vacation lake, finished in the middle of the rankings, largely because it isn't clear and has silt problems.

Bob White finished last, with East Lake in Osceola next. Coralville Lake, the heavily used fun spot near Iowa City, ranked in the bottom 10 percent with silt, runoff, clarity and low-oxygen problems.

Although weather fluctuations make it hard to see firm trends in lake water quality over the past 25 years, Downing said the data show that some lakes are clearly in trouble and need help.

"Iowans really love their lakes," said Downing, noting that 60 percent of Iowans said in a survey they go to at least one lake a year, usually several times at least. "This will help people with choosing which lake to go to."

Surveys by the Center for Agricultural and Rural Development at ISU have shown that people care about how clear the water is and whether it poses a health threat. People often are turned off by cloudy water, which also stops bottom plants from growing and makes it hard for fish to find food.

Downing's study also revealed a problem many don't associate with Iowa waters -- dead zones, which are called hypoxia by scientists.

Some Iowa lakes fight hypoxia, which causes fish to move to more oxygen-rich parts of the lake or die, Downing said. Plants can die, too. The lakes with the most low-oxygen trouble over the past five years included the U.S. Army Corps of Engineers reservoirs at Saylorville, Coralville, Rathbun and Red Rock.