Park Board officials explain elevated E. coli levels in Minneapolis lakes

Despite occasional spikes, officials say E. coli levels in Minneapolis lakes are generally low.
Despite occasional spikes, officials say E. coli levels in Minneapolis lakes are generally low.

Last week, the 32nd Street Beach on Lake Calhoun was closed followed a huge spike in E. coli levels -- in other words, there was an unsafe amount of crap (literally) in the lake.

THE BACKSTORY: E. coli closes Mpls beaches, prompts officials to warn against coming to beach while shitty

According to Park Board information, on July 15, two water samples taken near the beach averaged out to 12 E. coli units per 100 mL of water. But on July 22, that number jumped to a whopping 2,203 units per 100 mL. Since any test result above 1,260 prompts the Park Board to close a beach, Calhoun was shut down for a couple of days.But 32nd Street beach test results returned to the city two days later showed just seven E. coli units per 100 mL, and the beach was reopened.

What explains that huge fluctuation? According to Rachell Crabb, water quality supervisor for the Park Board, rollercoaster-like ups and downs are par for the course when it comes to E. coli measurements in Minneapolis lakes.

"There will be really low numbers, and rarely there will be a huge spike," Crabb said, adding that since she started working for the Park Board six years ago, she's been "surprised by how low our numbers are."

Crabb said that when the Park Board staff examined the 32nd Street beach, "there was nothing visual we noticed that was wrong -- other beaches had many more birds but lower bacteria levels, and there was a little bit of trash but nothing out of the ordinary after a busy weekend."

As the Park Board's website notes, "Increased bacteria levels predominantly come from waterfowl and pet wastes in yards, streets and parks that wash into lakes either directly or through the storm sewers as the result of a heavy rain." But it adds that "Elevated bacterial levels in lakes generally return to normal levels within 48 hours of a rainfall." That appears to be the case with Lake Calhoun's surprisingly high test result.

But that's not the story at the Lake Hiawatha beach, which was also closed last week. There, runoff from Minnehaha Creek, which extends all the way from Lake Minnetonka to Minneapolis, means the beach "has chronic problems due to storm water from almost all those suburbs west of the Cities flowing through to Lake Hiawatha," Crabb said.

Indeed, Dawn Sommers, communications manger for the Park Board, said staff debated whether there should be a beach at Lake Hiawatha in the first place since it seems "prone to closing once a summer."

There isn't much the city can do about that, but Crabb said staff has developed strategies for keeping E. coli levels as low as they possibly can.

"For example, we have our Porta Potties bolted down and facing in the direction where if they were vandalized, the impacts would be minimal," Crabb said.

That's good to know, because as Sommers put it, if elevated E. coli levels at Calhoun can be the result of something as seemingly innocuous as "geese or gulls lifting off," we'd hate to see what the meter would read if an entire Porta Potty was dumped near the shore.

-- Follow Aaron Rupar on Twitter at @atrupar. Got a tip? Drop him a line at [email protected]

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