Both Sandling and Beaver Dam beaches are closed.
Environmental engineers took more water samples Thursday morning. They have to get two back-to-back days of samples with acceptable amounts of the bacteria before swimmers can return.
It's believed the busy July Fourth weekend may be to blame.
"A lot of times people have babies with diapers in the water, and you're not supposed to do that," Environmental Engineer Jennifer Sjaardema said. "Also, the bacteria can settle to the bottom of the lake, and when you get a lot of kids playing in the lake, it can stir up this bacteria and bring it to the surface."
Ingesting that water can lead to some unpleasant effects.
"I think the most common [effect is] diarrhea," Sjaardema said. "If you have an open wound, it can make your wounds infected. You can get an ear infection, you can get respiratory infections."
It's the second time in a week Beaver Dam has been off limits. One City of Raleigh water expert told Eyewitness News the frequent closures are an indication of poorer water quality in Falls Lake.
However, Wake County officials contend the high bacteria counts are only found in the popular beach areas. The rest of the lake is fine and open for fishing and recreation.