Flathead Lake water quality remains 'high'

Visible water clarity is key to determining the health of a water body, and this fall Flathead Lake viewers should be able to see up to 17 meters below the surface.

With no big green algal blooms on the lake since 2008 and nutrient levels about the same as they were last year, water quality in Flathead Lake remains high.

That’s the word from Jack Stanford, director of the University of Montana’s Flathead Lake Biological Station. He addressed the Flathead Lakers at their annual meeting July 26.

“Water quality in Flathead Lake remains really high because we’re doing a really good job of controlling the nutrient loading from the Flathead Valley,” Stanford said. “This lake is on the threshold — if you add nutrients to the lake, it will get green, and that means the quality is less.”

Nutrients like nitrogen and phosphates from pavement run-off, fertilizing near water sources and sewage treatment plants help feed the algae that spread across parts of the lake in the past.

Flathead Lake’s water quality is also dependent on what is being taken out of the lake, Stanford said, because everything in the lake ecosystem has the potential to affect everything else.

Before mysis shrimp were introduced to Flathead Lake in 1977, the level of algae production in the lake was pretty low. But since then, algae production increased 30 percent and oscillated above and below that mark. When mysis shrimp numbers are lower than usual, the algae numbers drop and vice versa.

The shrimp are what Stanford calls a “strong interactor” — they affect the fish, and they affect the phytoplankton, which in turn affects everything else. But, Stanford notes, “It’s not that simple.”

To truly understand how everything interacts and how doing something like gill-netting lake trout affects the lake, Stanford said he needs to build a full-scale computer model. That would take a couple of years and about $1 million in funding.

The Flathead Lake Biological Station has gathered a significant amount of data over the last four decades that could go in the model. And they’re gathering more data than before from monitoring buoys placed west of Yellow Bay and west of Woods Bay.

“This is a major step forward in data monitoring,” Stanford said. “The data set is good and is repeating itself all the way to the ocean.”

So far, the data set shows Flathead Lake is healthier than most water bodies. The biggest reason, Stanford says, is that most of the water entering the lake comes from protected wilderness areas — Glacier National Park and the Bob Marshall Wilderness. But there are other threats.

“We’re in good shape on the pollution side,” Stanford said. “But that could be reversed if we get invasive species in here.”