BELLINGHAM - Scientific measurements of the biochemistry of Lake Whatcom showed some improvement in 2011, but that is probably the result of a cool summer, not human efforts to control polluting runoff.

So says Robin Matthews, the lead scientist on the annual lake water monitoring effort commissioned by the city. Matthews is director of the Institute for Watershed Studies at Huxley College of the Environment, Western Washington University.

"I think we got a break last summer," Matthews said.

Cold and cloudy conditions kept water temperatures lower, and that delayed and diminished the annual explosion of algae populations that have affected lake quality in previous summers.

In the hotter summer of 2009, the algae concentrations got so high that they caused a serious cut in the capacity of the city's water treatment plant, resulting in mandatory water use restrictions. But even in a cool year like 2011, the algae growth was still enough to reduce the system's capacity, Matthews said.

While the scientific measurements taken in 2011 did show a reduction in levels of phosphorus and algae, Matthews said she believes the reductions were minor, and the summer's lower temperatures probably account for those reductions.

"It (pollution measurement) is down a little but it's not down much," Matthews said. "It doesn't show an improvement from watershed changes."

Matthews refuses to draw conclusions from any single year's worth of lake water measurements. Instead, she points to the whole series of measurements going back to 1994. Those measurements show year-to-year fluctuations, but a general rising trend in both phosphorus concentrations and algae growth.

As Matthews explained it, the lake's problems stem from phosphorus-laden runoff that is made worse by human activities in the watershed. The phosphorus nourishes algae growth, and the dead algae become food for bacteria. The bacteria, in turn, deplete dissolved oxygen and make the lake less hospitable to fish.

And it becomes a vicious circle, because the lower oxygen levels result in chemical changes that release additional phosphorus from compounds and make it usable for algae food.

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Cool 2011 summer helped Lake Whatcom water quality a bit