CHICAGO (CBS) — An increase in bacteria levels in Lake Michigan has resulted in some warnings for swimmers.

Severcal Chicago beaches have swim advisories due to increased levels of e Coli.

Beaches in Evanston are temporarily closed due to high bacteria.

Before you head to the beach, you can check Chicago’s beach report.

E. coli occur naturally in the fecal waste of humans and other warm-blooded animals. Some strains can be harmful, and they can indicate the presence of other disease-causing bacteria.

A variety of factors can cause E. coli pollution, including illegal sewer connections or discharges, malfunctioning sewer systems, storm runoff after rainfall, or even swimmers pooping in the lake, the City of Evanston said.

The bacteria will dissipate as a result of natural die-off, wind and wave action, or ultraviolet light from the sun.