TWIN LAKES - High levels of E. coli bacteria have been measured at North Twin Lakes beaches throughout the past two months, the most recent samples showing lowered levels.
Officials with the Iowa Department of Natural Resources said they may have found and fixed the cause.
A stockpile of horse manure was identified as a possible source of the problem, said Ken Hessenius, supervisor of the Spencer DNR field office.
"It appeared to be coming from a tile, so someone went down and looked at it. From what we could tell, the only real potential source ... was a fenced-in area that contained some horses," Hessenius said.
"The area had received a fair amount of rainfall, and there was some runoff from that lot, and in that development area there was an intake. The water that ran through the feedlot made it into the intake, and that intake discharges fairly close to the beach, on the lake.
"We visited with the landowner, and they, within that same day I believe, had plugged that intake so no more runoff from the feedlot would get into it. And I think they did some cleanup of some stockpiled manure, so that should take care of it. Plus, the horses went out to pasture, so they're not in that confined area anymore."
Twin Lakes water test levels
May 20: Treman Park, 160,000 E. coli per 100 ml; State Park West, 910 E. coli per 100 ml; State Park East, 85 E. coli per 100 ml.
May 28: Treman Park, 1,200 E. coli per 100 ml; State Park West, 86 E. coli per 100 ml; State Park East, 63 E. coli per 100 ml.
June 3: Treman Park, 450 E. coli per 100 ml; State Park West, 110 E. coli per 100 ml; State Park East, 140 E. coli per 100 ml.
June 10: Treman Park, 9,200 E. coli per 100 ml; State Park West, 52 E. coli per 100 ml; State Park East, 10 E. coli per 100 ml.
June 17: Treman Park, 41 E. coli per 100 ml; State Park West, 10 E. coli per 100 ml; State Park East, 20 E. coli per 100 ml.
June 24: Treman Park, 5,500 E. coli per 100 ml; State Park West, 5,800 E. coli per 100 ml; State Park East, 2,100 E. coli per 100 ml.
Brandon Miner, one of the DNR inspectors, said they looked around but did not find any other problems.
Calhoun County Conservation Director Keith Roos said the property belonged to Stephanie Chase. Miner said there was no record of the DNR being out at that property before. Roos said he's never been involved in anything there.
Miner said he visited the property on May 31 and the tile was plugged within the next day, and the manure stockpile has now been removed.
"I've spoken to Keith Roos and the owners, and they've confirmed it's out of there," Miner said on Wednesday. "They moved most of it about a week and half ago, and just finished in the past couple days.
"We're hopeful this takes care of it."
On May 20, the DNR reported a bacteria result of 160,000 E. coli per 100 milliliters of water at Treman Park. State guidelines list 235 E. coli per 100 milliliters as the maximum safe level in any given sample.
The most recent sample was on Monday. It found 63 E. coli per 100 milliliters of water at Treman Park, 52 at the west Twin Lakes State Park beach, and an undetectable amount - less than 10 bacteria - at the east state park beach.
"They're surprisingly low this week," said Jason McCurdy, DNR beach monitoring coordinator. "Just showing how variable it's being up there. A big part of it is I don't think there was any rain before we sampled, so I think that's a huge help."
Bacteria levels at Treman Park exceeded safe guidelines more often than not throughout June. Just one week before Monday's sample, the level at Treman Park had been 5,500 E. coli per 100 milliliters of water.
"The bacterial quality of the water is kind of wonky right now," McCurdy said. "I think rain is a big driver. If we don't get rain before we sample, it doesn't get washed in. Apparently it doesn't stick around long after does get in there, which is good."
McCurdy said even though high bacteria levels were found after the tile was plugged, the manure still could have been at fault.
"Not knowing exactly what was done or being that familiar with how the rain runs off from that particular pasture, I can't really speak to it," he said. "With the heavy rains we were getting, even if that tile was blocked, that's not to say runoff from that pasture was being stopped from reaching the lake.
"It could still be coming from the pasture, or could be that plus another source."
If the problem persists, McCurdy said the DNR and county conservation office will have to decide what steps to take next. Weekly samples will be taken until Labor Day. The results are available at http://is.gd/IAbeaches.
The two state park beaches remained under safe levels except for the sample taken on June 24.
The DNR combines the five most recent samples in a 30-day period into a geometric mean, McCurdy said.
"It gives more of a trend, of what the bacteria water quality is doing," he said.
If the geometric mean goes above 126 E. coli per 100 milliliters of water, the DNR posts a warning that swimming is not recommended.
This never happened at the state parks, so an advisory was never issued, McCurdy said, even though the June 24 samples at both beaches were high.
The geometric mean is currently 567 E. coli per 100 milliliters of water at Treman Park.
Shelly Schossow, of Calhoun County Public Health, said swimming should be fine at the state beaches as long as it doesn't rain.
"It goes up and down, and it seems to correlate with the rain," she said.
McCurdy said, "If it doesn't rain, the levels should remain low. If it does rain, I would definitely recommend people avoid the lake for 24 to 48 hours."
Schossow said E. coli is just one of many species of harmful coliform bacteria.
"A lot of them can cause gastro-intestinal illness, vomiting, diarrhea, and they can cause infections in open sores," she said. "It can make people and animals sick. If people take their dog, it's obviously going to drink the water, and that will make them sick."