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Policy changes to help city better identify toxins in Lake Mitchell

Daily Republic - 8/14/2019

Aug. 14--There's a new way to test for harmful bacteria and toxins looming in Lake Mitchell.

That's according to Parks and Recreation Director Nathan Powell, who said the Environmental Protection Agency (EPA) recently announced new standards and improved technology that allow for more discrete testing.

"With the new standards, we no longer have to test for chlorophyll. We will now have to test for the two toxins: cylindrospermopsin and microcystin," Powell said in an interview with The Daily Republic. "The improved science technology that the EPA has developed will greatly help us monitor the toxin levels at the lake."

The Parks and Recreation Department has implemented the new technology with its decision to welcome on-site water quality test kits that have been used at the lake for the past month. Powell said the test kits eliminate the city having to submit the water quality samples to the state's EPA agency, which would take up to a week to receive the results. The Parks and Recreation Department practices weekly water quality tests, which take place every Monday throughout the summer months.

"The on-site testing has been going well, and it helps us get the results of the toxin levels right away," Powell said. "We can now get the information out to the public sooner than later."

By not having to test for Chlorophyll, Powell said the Parks and Recreation Department's water quality tests will examine the toxin levels of microcystin, which was previously gauged through the testing of Chlorophyll.

According to Powell, when the Chlorophyll was up the microcystin was either right at the same level or a little under, which produced inaccurate levels at times.

The two toxins that exist in Lake Mitchell -- which the city of Mitchell tests for -- are cylindrospermopsin and microcystin, which are a form of cyanobacteria, also known as blue-green algae. They both can produce toxins in recreational waters and have been found to cause human and animal illness.

According to Powell, the cylindrospermopsin levels must be at or above 15 parts per billion (ppb) for the city to issue a public health warning. Parts per billion is the units of measure the Parks and Recreation Department uses to calculate and identify the concentrations of the two contaminants or toxins.

The city's policy for a public health warning at Lake Mitchell discourages direct contact with the lake but doesn't call for the closure of the lake, while a public health watch only discourages the specified portion of the lake where microcystin levels are above 4 ppb.

As of the most recent water quality test, Powell said Lake Mitchell's cylindrospermopsin level came in at 1.6 ppb, while the microcystin levels were right at 4 ppb, which caused the most recent public health watch at Lake Mitchell. Powell said the lake's cylindrospermopsin levels have only risen above 4 ppb in the previous two years, excluding this year's 1.6 ppb level.

"The rainfall has seemed to help keep the toxin levels at a lower rate than in previous years when it was very hot," Powell said. "The microcystin levels are what we're monitoring more closely this year, because the cylindrospermopsin have been consistently low."

The city also tests for e-coli. Powell said the tests use the same levels of e-coli -- which is 235 colony forming units (cfu) per 100 milliliters -- to determine whether a public health warning should be issued. However, the policy change calls for closing the specific location of where the harmful e-coli level was found; rather than closing the entire lake like the previous policy mandated.

"We test for e-coli at the beaches primarily, so the new change will have us close the beach and not the entire lake," Powell said. "We've had two e-coli levels reach above the 235 cfu in the past four years, but it could be from bird feces in that area, so it doesn't mean the whole lake has harmful levels of e-coli."

According to Powell, a public health warning will only be issued when microcystin toxin concentrations are greater than or equal to 8 ppb in any testing location, which used to be 20 ppb. In addition, if the cylindrospermopsin concentration is greater or equal to 15 ppb in any testing location, a public health warning will be issued.

"We will only be putting out a public health warning if there is a toxic problem," Powell said. "We won't be putting out any warnings if there's not."

By switching to the new policy guidelines, Powell said it will help protect the public, while alleviating constant calls for alarm.

While City Council member Marty Barington backed the policy change, he suggested the city issue a notification when the toxin levels reduce below the harmful levels.

"It's obviously a good practice to issue advisories when the toxin levels are at harmful warning levels, but when they lower to a safe level I think it's a good idea to get the word out the lake water quality is good again," Barington said. "Because if we don't notify people that the lake is safe, then we risk people swimming in the lake and deciding not to camp at the Lake Mitchell Campground."


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