A swimming advisory has been issued this week for Grand Glaize Beach at Lake of the Ozarks State Park due to high bacteria levels.

A swimming advisory has been issued this week for Grand Glaize Beach at Lake of the Ozarks State Park due to high bacteria levels.

Water samples taken June 19 from the Osage Beach area public beach tested above the state advisory level for E. coli with a geomean result from two samples of 1,061.2 mpn/100 ml. The individual results from each sample were 488.4 and 2,419.6.

The advisory indicates swimming is not recommended.

While bacteria levels were high at GGB during this week’s sampling, Lake of the Ozarks State Park Public Beach #1 showed very low bacteria levels at the time of testing with a geomean of 2.5.

Elevated bacteria levels are frequently associated with heavy rains, however, there are a number of other sources that may contribute to elevated bacteria levels, which may pose a health risk, according to the Missouri Department of Natural Resources which is responsible for the testing.

It is common for bacteria levels to spike temporarily in early summer due to renewed use of the beaches for the season. Beach-goers stir up sediment which hosts bacteria from wildlife that has dropped down throughout the off-season.

Once the sediment is stirred up, however, the natural flow of the lake dissipates the bacteria and E. coli levels go back down.

As unpopulated natural areas, state park beaches commonly see numerous geese and other wildlife.

In state park water quality testing elsewhere in the state, a swimming advisory was issued for Cuivre River State Park Lake Lincoln Beach - northwest of St. Louis - which had a bacteria level geomean of 414.

Harry S Truman State Park Campground beach and Lake Wappapello State Park Public Beach are both closed due to flooding.

3 things to know about state park water quality testing

1. The level of e. coli that requires notification

The maximum limit for an advisory to be issued is a geometric mean of 190 mpn/100 ml based on EPA guidelines. The geometric mean is found by multiplying the results and taking the fifth root. Sampling is done once a week on Monday or Tuesday to have results posted for the weekend. The status of the beaches is posted on location as well as online. Go to http://dnr.mo.gov/asp/beaches/to see results each week for the 18 state-owned beaches in Missouri.

2. Beaches are not closed if the limit is exceeded.

If levels are over 190 mpn/100 ml, swimming is simply not recommended. The state posts the most recent test results whether the level exceeds the limit or not. DNR can close the beach if a documented health risk is known - such as flooding, debris or some kind of spill. State beaches can also be closed if E. coli levels max out the state’s computation system: 2,419.6 e. coli colonies per 100 milliliters of water. If that would occur, it would be an administrative decision whether to close the beach.

3. E. coli testing takes 24 hours, so it cannot be known what the level actually is on any given day.

At most, it can only be known what the bacteria level was yesterday. Posting the level of bacteria helps beach-goers make their own decision about how safe the water is for swimming. There are other factors to consider though, including recent rainfall events and subsequent contamination, personal health issues that lower your immune system and potential pollutant sources nearby.

While high results one day can be a predictor that the levels will be elevated the next, there can also be a runoff event or other incident that causes the bacteria level to spike after the weekly testing shows low levels. One general safety rule when swimming under any conditions - whether in lakes, streams or swimming pools - is to avoid swallowing water.

In natural recreational waters, some level of bacteria is always to be expected, and even swimming pools can be hazardous due to the time it takes for chlorine to kill bacteria.