Understanding Bacteria in Lakes

Understanding Bacteria in Lakes

A dip in the lake can be refreshing, but it’s important to consider what’s going on in the water that you may not see – especially for E. coli bacteria.

Identifying an E.coli issue

It’s fairly easy to see Harmful Algal Blooms (HABs) and algae at a lake.  Unfortunately, the same visual assessment does not apply to E. coli.  However, there are three indicators of E. coli in a lake to consider:

1. Recent rain. When it rains, water runs over the ground, picks up E.coli and carries it to ponds, lakes, streams and rivers.

2. Large presence of waterfowl. Bird feces contribute both bacteria and pathogens to the water.

3. Many people.  There’s a correlation between the number of people at beaches and high bacteria counts in the water.

Quanta Tray

A Quanta Tray is used to analyze E.coli bacteria counts. The neon glowing cells indicate the presence of E.coli. The number of glowing cells are counted and a statistical formula is used to calculate the amount of E.coli Present.

Beach Closings and Bacteria

Public beaches in Nebraska do not close when bacteria counts are high. Bacteria counts can rise and fall very rapidly. Bacteria is very susceptible to UV light, i.e. sunshine. So on rainy cloudy days bacteria counts are high, while bacteria counts drop on bright sunny days. This change happens rapidly.  As a result, Nebraska does not close beaches when the count is high.  The bacteria sampling at public beaches, instead, allows individuals to make informed decisions about where to recreate based on the most recent results.

E.coli and Sickness

The most common issues with E.coli ingestion is gastrointestinal distress – stomach flu-type symptoms. These are typically not life threatening, although more serious issues could arise. E. coli bacteria levels measured above 235 colonies/100 ml are considered a higher risk for illness when swimming.

This article was reviewed by Mike Archer, Nebraska Department of Environment and Energy

Sign up for updates from UNL Water

Sign Up Here