How deep does Capitol Lake need to be to be healthy? 300 feet.

algea lake How deep does Capitol Lake need to be to be healthy? 300 feet.Every summer Capitol Lake is blanketed with a thick layer of green algae. While it obviously unsightly, it is also a sign of a sick body of water. The algae growth indicates an unbalanced system, a stagnant, warm lake that has too much phosphorus for its size and shape.

A lot of people think it would be an easy fix to get rid of the algae, just dredge the lake back to where it was in the 1980s. But, the reason the lake was clear of algae back then was because of saltwater flushing. This practice was ended years ago because of obvious impacts to water quality in lower Budd Inlet.

To really get rid of the algae every summer with dredging, you would need to go deeper than 13 feet. Way deeper. Like 300 feet.

Seriously, 300 feet.

This fact is explained in a letter from the state Department of Ecology in 2009 to the then Department of General Administration. A GA staffer asked DOE what the impact would be of dredging to 13 feet on several water quality factors:

What would be the effect of implementing both the shading improvements and the lake dredging on the lake and Budd Inlet relative to the five TMDL water quality factors (dissolved oxygen, temperature, PH, fecal coliform bacteria and find sediment)?

The answer:

Combining upland improvement 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 are expected in Budd Inlet either.

You can read the entire letter here.

Capitol Lake is eutrophic. Meaning, in the case of Capitol Lake, there is extremely low dissolved oxygen and annual algae blooms.

For both the current and dredged lake alternatives, the combination of phosphorus loading and lake geometry plots wells into the eutrphohic zones… The dredged lake alternative would still fall well into the eutrophic range, either for the annual loading or for only the summer loading rate.

Without reductions in the areal phosphorus loading rate, the lake depth would need to be >100 m (300 feet) to fall into the mesotrohpic (or healthy) range… With the propoposed nominal depth of 14 ft (4.0 m), the annual areal loading rate would need to be reduced one to three orders of magnitude to achieve the mesotrophic range.

The problem is then, that 75 percent of the sediment load (which carries algae causing phosphorus into the lake) is natural. So, even under natural conditions, Capitol Lake is too shallow would never be healthy.

But, why isn’t there the same phosphorus problem with an estuary?

Well, simply put, places like Budd Inlet are supposed to get a lot of phosphorus. Most of the phosphorus coming down the watershed is natural and it always used to end up in Budd Inlet with no ill-effects (this is shortly described in a GA document here.

What is unnatural is trapping it in a shallow, stagnant lake. That causes algae blooms and low dissolved oxygen. Letting the natural phosphorus load go naturally out into the saltwater doesn’t cause the same thing to happen.

Capitol Lake is the major cause of low dissolved oxygen in Budd Inlet

Budd Inlet has a dissolved oxygen problem. In short, there isn’t enough oxygen in the water near Olympia to support healthy marine life.

And, the primary reason for this dramatic drop in oxygen is Capitol Lake.

Recent findings released by the state Department of Ecology point out that even if all of the other problems that cause low oxygen went away (other than the lake), most of the problems in Budd Inlet would still exist.

Low dissolved oxygen is important because fish and other marine life need enough oxygen to live. Capitol Lake is shallow, stagnant and fills each summer with algae, so the water flowing out of it is extremely low in dissolved oxygen.

Some people have argued that the real problems we face in deep South Sound have don’t have anything to do with Capitol Lake. But, as the results from Ecology show, even if we moved the LOTT treatment outfall to Priest Point or Boston Harbor, implemented advanced treatment at waste water treatment plants and reduced all other influences on dissolved oxygen, Capitol Lake is still the biggest problem.

These maps shows all of the parts of southern Budd Inlet that violate water quality standards. Each colored area (from blue to red) indicates by how much water quality standards are violated. These maps were presented at the most recent meeting of the Deschutes watershed TMDL advisory committee.

This is current conditions, with the lake in place and a host of other issues:

Current day 207x300 Capitol Lake is the major cause of low dissolved oxygen in Budd Inlet

This is the map if everything else was cleaned up and just the lake remains:

Lower Budd just the lake 202x300 Capitol Lake is the major cause of low dissolved oxygen in Budd Inlet

And, this is the map if the lake was removed and the rest of the problems were taken care of:

Current condition no dam 209x300 Capitol Lake is the major cause of low dissolved oxygen in Budd Inlet

Clearly what happens when you try to clean up the rest of the issues and just leave the dam is that the dissolved oxygen problem remains. You’ll still have some issues if you do nothing else and take the dam out, but Capitol Lake is clearly the leading cause of low dissolved oxygen in Budd Inlet.

Originally posted at the Squaxin Island Tribe’s natural resources blog.

The history of the Deschutes River estuary, 1895 to 1948

How the Deschutes River estuary came to be dammed in the 1950s has been a heated topic locally the last few years. A history of the local efforts to dam the estuary and create Capitol Lake is now available.

The history covers the time from just after statehood when the first dam was proposed to just after World War II when the funding for Capitol Lake became available. The piece refutes the position that the lake was entirely inspired by the “City Beautiful” design of Wilder and White in the 1911 proposal for the capitol campus.

History of the Deschutes Estuary, 1895 to 1948:
Google docs format
PDF format

Also available is the total works cited for the history
Works cited
Other related materials