If you're going to take a dip in a lake this summer, you might want to wait before diving in after a big rain.

That's usually when bacteria levels are at their highest and when most beaches are forced to close temporarily due to high bacteria count.

In East Central Illinois swimming holes are few — rare, actually — but if you need a break from swimming in a pool, there are a couple options. Before you go though, you might want to check the Illinois Department of Public Health's beach watch website, to make sure it's not closed, or better yet, call the park itself.

Pools certainly are popular but "personally I think the beach is coming back. Our beach has been busy in the last couple years. It's busy every weekend," said Matt Kuntz, the site superintendent at the Middle Fork Forest Preserve near Penfield, managed by the Champaign County Forest Preserve District.

The man-made Willow Pond, almost 5 acres in size, is inside the park's campground and open to everyone.

Last year the park had two tests that came back positive for high bacteria: one in mid-June and the other in August. That was the first time closings had happened in at least the seven years Kuntz has been working there, he said.

"In June it was probably because of the rainfall. Before we sent the samples in we received up to 16 inches of rain in a period of two or three weeks. That also happened in August," he said.

The swimming beach on Clinton Lake in DeWitt County was closed for two days when the season opened this year and it was right after a heavy rain, said Kayla Wilson, owner of Boondocks in the Mascoutin area of Clinton Lake. The business manages the beach and shower house and also rents inner tubes and other items for swimming there.

"We've been pretty busy this year. On a good day we'll have 600 to 800 swimmers," Wilson said.

Earlier this month the Willow Pond swimming beach at Middle Fork Forest Preserve was erroneously listed as being closed on the Department of Public Health's website. But it has been open for swimming since this year's swimming season began. No tests have turned up high bacteria since last year.

The mistake has been corrected and department of public health staff are working on updating the website with test results as quickly as possible, a department spokeswoman said. Ideally staff at labs where the bacteria tests are conducted will be able to update the website directly.

Also one day, ideally, the state's beach waters will be analyzed using rapid testing, which would produce results within minutes instead of the current culturing method which takes about 18 hours, said Justin DeWitt, chief of general engineering with the Illinois Department of Public Health.

The department licenses swim beaches, except for those on Lake Michigan operated by local municipalities, under the Swimming Facility Act. Managers of the beaches send in samples every two weeks to labs around the state.

"Typically beach water is tested only for E.coli. The reason is it's widely recognized as an indicator bacteria. When we see E.coli high, other bad bugs typically are high as well," DeWitt said.

As long as levels are below 235 CFU (or colony-forming units) per 100 milliliters of water, they're OK to be open for the next two weeks, he said. If the beach water tests above that level, the beach needs to have two consecutive samples below the 235 level in order to reopen.

"Usually inland beach quality is driven by rainfall," and usually the levels will return to normal after a few days, DeWitt said. The rainfall may cause turbulence in the lake or pond, stirring up sediment and suspending more bacteria. Or water runoff may discharge into the lake, he said.

Another issue: animals.

"Geese carry a lot of bacteria; their feces make a mess of a beach," DeWitt said. Some beaches are chronically closed for this reason.

According to the department of public health, gastroenteritis is the most common illness associated with swimming in polluted water. Gastroenteritis is caused by germs such as Cryptosporidium, Giardia, Shigella, norovirus and E.coli. Symptoms can include chills, nausea, diarrhea, stomach ache, headache and fever.

In addition to avoiding going swimming after a heavy rain, the department recommends swimmers look for storm drains (pipes that drain polluted water from streets) along the beach and don't swim near them. Also look for trash and other signs of pollution such as oil slicks in the water, the department advised.

"We recommend any time you're going to public park to call ahead and make sure know what its status is," said Chris McCloud of the Illinois Department of Natural Resources.

Other nearby beaches include several at Lake Shelbyville (Dam West, Sullivan Beach, Wilborn Creek and Wolf Creek State Park), Moraine View State Recreation Area in LeRoy and Clinton Lake.