One of the most important issues surrounding the future of the Deschutes Estuary and Capitol Lake is how the various options being considered (see my previous post) will impact water quality.

How will restoring the estuary improve water quality in lower Budd Inlet? Can we make changes upstream of the current lake to improve water quality in the lake?

These are all questions being considered by the Capitol Lake Adaptive Management Plan committee as we consider a recommendation on whether to restore the Deschutes River estuary. And, a recent letter from the state Department of Ecology to the Department of General Administration (which owns the property around the lake and therefore manages it) sheds a lot of light on the water quality debate.

In short, the letter spells out the water quality problems in Capitol Lake are being caused by the lake’s very existence. Because the artificial lake is by its very design shallow, warm and sluggish it becomes a haven for algae growth that leads to its many water quality problems.

The designers of Capitol Lake wanted a peaceful and tranquil reflecting pond. Unfortunately, those considerations also create low oxygen levels, warm water that is unsafe for fish and other water quality problems. The only real way to address Capitol Lake’s water quality problems is to return it to an estuary.

The letter from Ecology to General Administration answers several questions staff from one agency had for the other. The questions centered around the “managed lake” option, the option that would attempt to continue the management of the lake as it had been for the better part of 50 years.

To the question of whether controlling temperature of the Deschutes River above the falls would lead to lower temperatures in the lake, Ecology staff respond:

Decreased river temperatures would not translate through the middle basin to the highly productive north basin… Additional model runs could quantify any benefits, but watershed actions are not likely to resolve water quality issues within Capitol Lake or Budd Inlet.

In short, no matter how well you restore habitat above the lake, the very existence of the lake causes its own water quality problems.

Another question from GA asks whether combining upland shading with lake dredging would improve water quality. DOE responds:

Combining upland improvements and deepening the lake also would not resolve water quality issues within Capitol Lake… Because Capitol Lake currently and under the dredged lake alternative falls well within the eutrophic range, based on available indices, these improvements are unlikely to translate into measurable or significant lake improvements. No changes to Budd Inlet are expected either.

The problems that are created by Capitol Lake flow down into Budd Inlet. Lack of oxygen in the water and increased water temperatures stand in the way of restoring that part of Puget Sound. By keeping a section of the Deschutes Estuary damned up, we’re agreeing that we’re ok with bad water quality.

Here is a link to the letter.