TWIN LAKES - The bacteria level at one of the Twin Lakes is coming down, but is still higher than acceptable, according to officials, who say people should stay out of the water there.
High levels of bacteria at Treman Park, on the north shore of North Twin Lake, caused concern last week. However, bacteria levels always go up after heavy rains, officials say, and new results show that levels are beginning to drop.
The Iowa Department of Natural Resources reported a result of 160,000 E. coli bacteria per 100 milliliters of water at Treman Park from a May 20 sample.
"That's a very high level, the highest I've seen in a beach I've monitored during my time at DNR," said DNR Beach Monitoring Coordinator Jason McCurdy.
State guidelines list 235 E. coli bacteria per 100 milliliters as the maximum standard level, McCurdy said.
A sample taken on Tuesday showed the level had fallen to 1,200 E. coli at Treman; results from the sample were first available Thursday.
Two other Twin Lakes beaches are also tested by the DNR, one at the State Park located on the east side of the lake, and the other just across the lake on the west side. The west beach showed 910 E. coli May 20, while the east beach was within safe limits at 85 E. coli. On Tuesday, the west beach had dropped to 86, and the east beach to 63.
Keith Roos, Calhoun County Conservation director, said a caution sign was posted at Treman Park on May 24, the same day he got notice of the situation.
No signs were posted at the west beach, McCurdy said, because the Twin Lakes beaches are considered less vulnerable. This means that in the past, whenever bacteria levels have peaked they dropped back down quickly.
"Our policy dictates that for less vulnerable beaches we don't have to post an advisory, because historically the bacteria problems aren't persistent," he said. "We've seen they've already dropped back."
Roos said the high bacteria levels came from the heavy rains.
"More than likely it's the high inflow of water with all the rain we had," said Roos. "A lot of times you get a spike like that after a heavy rain event, and I would guess it will subside."
The DNR took over monitoring the lake about three years ago, he said. Prior to that, Roos was involved in testing.
"In the number of years I did the testing, I think we had one other high bacteria event, that I can remember," he said. "That time, it was a one-week event, and the next test I took the next week came back fine. With all the rain, it may be a longer time period, I'm not sure."
Swimming is never recommended within 24 hours after heavy rainfall, McCurdy said, because the rainfall washes bacteria into waterways.
"If you do go swimming, be sure to shower after, limit your time in the water, and - I tell people if the water looks turbid or nasty, don't dunk your head, because that is the principle route for introducing those bacteria that make you sick," he said.
McCurdy said a spike like this could come from any number of things, from agricultural runoff to leaking septic systems to wildlife. The quick drop suggests to him it's not leaking sewage.
"If the problem persists at high levels, or if it persists after quits raining, I would think it's a point source like a broken sewer, but if it drops it's probably a non-point source," he said.
In addition to the 235 bacteria per 100 milliliter maximum, the Iowa DNR website also states that the average value of five tests over a 30-day period should not exceed 126 E. coli per 100 milliliters. Five results have not yet been reported this year.
The results for this and other beaches throughout the state are available from the DNR Beach Monitoring Hotline, (319) 353-2613.