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Worried about Lake Lanier being — icky? Here’s what you should know before you swim
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A couple ride a personal watercraft Friday, May 27, 2022, on Lake Lanier near Thompson Bridge Park. - photo by Scott Rogers

Is it safe to swim in Lake Lanier this Memorial Day weekend? 

If you’re thinking about that in regards to water quality, the answer is, probably by Sunday. But to avoid harmful bacteria in the water throughout the summer, these are some things visitors should know. More worried about boat safety? Here are some tips about that.

Don’t swim after heavy rain

Chattahoochee Riverkeeper Jason Ulseth said visitors should be careful if there have been heavy recent rains and if the shore is near a tributary. 

“The No. 1 source of pollution to the Chattahoochee and Lake Lanier is stormwater runoff,” Ulseth said. 

Most of the time, if the water looks clear, then it is safe to swim, he said.

“If it looks like chocolate milk, then that can be an indicator that you have a stormwater influx coming in that could be carrying contaminants like E. coli,” Ulseth said. 

Each shore is slightly different. Shores closer to a creek or tributary are more likely to carry pollutants, while isolated shores are more likely to be safe. 

Runoff can lead to high E. coli levels in certain areas of the lake, which can cause illness. Symptoms include vomiting, rashes, diarrhea and eye and ear infections, Ulseth said. 

Testing for E. coli

Chattahoochee Riverkeeper tries to measure E. coli levels weekly at a few dozen shores in Hall County during the summer.

E. coli is the best indicator of the presence of pathogens in surface waters, and its presence provides direct evidence of fecal contamination of the water, according to the U.S. Environmental Protection Agency. 

At some parks around Hall County, residents can find the latest E. coli levels via water safety signs that have a QR code linked to the riverkeeper’s data page

South Hall Rotary helped fund the signs, which were put up over the last month at River Forks Park, Laurel Park, Cherokee Bluffs Park, Williams Mill Greenspace, Cedar Creek Reservoir and Wahoo Creek Park. The organization hopes to install more safety signs in Gainesville and other areas around the lake, said Amanda Groover of South Hall Rotary. 

On the site, people can click on shores throughout much of the Chattahoochee River Basin to see E. coli levels, turbidity (a measure of the water’s clarity) and rainfall over a period of time. 

Understanding the data

For E. coli testing, more than 235 MPN per 100 mL is high for one test, Ulseth said. 

“(At that level) if you had 1,000 people that had full contact with the lake, completely submerged — ears, nose, mouth — 36 of those 1,000 people would contract some kind of illness,” Ulseth said. 

The Environmental Protection Agency sets a standard that over a month, an average level of 126 parts per 100 mL are high and warrant monitoring closely. The levels shown on the site are best used to show the overall health of a shore over time, Ulseth said, rather than a point-in-time test. 

Test results aren’t available until at least 18 hours after the water sample is collected, he said. 

Bacteria levels typically decrease within 24 to 48 hours after heavy rainfall, Ulseth said. 

If a shore is consistently testing high for E. coli levels, it is called a “hotspot,” and riverkeeper staff may have to investigate further, Ulseth said.

“We put on waders, we jump in the creeks, and then we walk up and test in increments … until we find the source,” he said. 

Despite lots of rain this past week, Ulseth said he would expect waters to be safe by Saturday or Sunday just in time for Memorial Day.