Lake Champlain looks murky, but experts say it’s too soon to know the flood’s impact

Last summer, in the week after a deluge of rain fell on Vermont and caused extreme flooding, rivers carried almost as much sediment and pollutants into Lake Champlain as they typically send in a year .

Seven days after last week’s extreme flooding, scientists are just starting to compile data to understand how the heavy rain and resulting runoff impacted the lake this time.

The latest extreme weather “exacerbates the concerns we saw last summer,” Julie Moore, secretary of Vermont’s Agency of Natural Resources, said at a press conference Tuesday in Berlin.

She expects to see similar statistics about pollution from flooding this year, particularly related to the Winooski River, though she added the pollution might not be as widespread.

Until scientists are able to analyze the data from last week’s storm, according to Matthew Vaughan, chief scientist at the Lake Champlain Basin Program, several other factors give clues about the current health of the lake.

“With this storm, we have very turbid water, meaning low water clarity, or a lot of sediment suspended in the water,” he said, adding that plumes of sediment from different rivers have combined and reduced the overall clarity of the lake.

The turbid water can prevent some natural processes from playing out, according to Vaughan: Plants and other life at the base of the food chain can’t access sunlight to photosynthesize, for example, and aquatic predators might struggle to see and catch their prey.

It could also make wood and other debris from the flood hard to see, posing a danger to boaters and other people recreating in the lake.

On the other hand, turbidity could shield toxic cyanobacteria from sunlight, which it needs to bloom, he said. Cyanobacteria blooms often cause beaches in Burlington and elsewhere to close in the summer.

Last year, the turbidity cleared after about two weeks, Vaughan said, and then “things got back to normal. So that’s not going to have a lasting impact on the lake,” he said.

However, an excess of nutrients, such as phosphorus, could spell trouble for efforts to remediate water quality that have been ongoing for years. The federal Environmental Protection Agency mandates an annual limit for the amount of phosphorus that can enter Lake Champlain, called a total maximum daily load, and the state has been making tepid progress toward those goals.

Moore said the Agency of Natural Resources is conducting a broader analysis of water quality data to look at long-term trends and understand whether the agency needs to change its approach to managing water quality.

“This is a concern for us, as climate change is going to continue to cause more intense and more significant wet weather events,” she said Tuesday. “Our water quality clean water goals for Lake Champlain need to be achieved regardless of climate change.”

In the immediate future, swimmers should be cautious while swimming in the lake, Vaughan said. Right now, it’s safest to swim in areas of the lake that are being consistently monitored for cyanobacteria and E. coli, he said.

On Wednesday, all of Burlington’s beaches were safe for swimming and recreating, according to the city’s website, and all state parks other than the Alburgh Dunes were open .

Several Burlington beaches did close due to high E. coli counts in the days following the flood.

The lake could also hold other pollutants washed off the land during the storm, though “those contaminants would be very, very dilute to the point of likely not having an impact on water safety” in Lake Champlain, Vaughan said.

As Vaughan tries to understand how flooding impacts the lake, he noted the effects of climate change, which is “impacting everything that we do to try to restore and protect water quality.”

“This is a great example of how climate change is impacting our watershed,” he said.

Read the story on VTDigger here: Lake Champlain looks murky, but experts say it’s too soon to know the flood’s impact .