Lake Is Full of Algae This Summer

Observation by Gillian Brubaker:

Back in the early 70s, Cheney Lake was a gravel pit used for building the Minnesota Bypass. Later after it was flooded by springs at the north end of the lake, it was established as a city park. There has always been some algae in the lake, developing mats that float on the surface. But this year, the algae is the worst I can remember. What kind of algae is this? I think it is choking the lake. Also, there seem to be two layers of algae this year. One on the surface and one growing up from the bottom. This worries me because it is spoiling the recreational value of the lake, you can hardly paddle a boat through the algae. It is also a sanctuary for many kinds of birds. The lake is also stocked with salmon and many people enjoy fishing here. But you can hardly cast a line with all of the algae. Many people use the trails around the lake, walk their dogs and let them cool off in the water. I wonder if the algae and the water is dangerous for the animals, or the fish. I am worried that unless we do something, the algae bloom will kill the lake, or at least our enjoyment of it.

Mike Brubaker with the Alaska Native Tribal Health Consortium, writes:

Cheney Lake is located in East Anchorage in a residential area. It is not connected to any streams but does have springs in the northeast corner that feed the lake. It is surrounded by homes and hosts a lot of waterfowl during the warm months and even in any open water into the winter. Over the years, it has grown into a popular park area with walking trails through the woods. People fish year round and ice skating is popular in the winter. As my mom indicated above, the lake was once a barren gravel pit. As kids, we would swim and play in the lake, sometimes we would have great fun hurling snail-covered algae mats at each other. There were homemade rafts built out of wood and 55-gallon drums which were paddled around the lake using boards for paddles. If you were brave, you jumped in. The lake was not stocked with fish, as it is today, but there were lots of sticklebacks, and of course the snails. So we have been aware of the water quality problems at Cheney for a long time. This year however, the conditions look particularly bad, with large mats of algae on top and under the water.

We learned more about the water quality in the early 1990s. Samples collected by the Municipality from 1991 to 1994 showed that the levels of coliform bacteria exceeded acceptable levels in every month of the year (see attached document from Environmental Protection Agency). It was placed by Alaska Department of Environmental Conservation on the list of "impaired water bodies." The source was thought to be the goose population, runoff from storm water, and runoff from pet waste. The combination of a city-wide goose population control program, and the Municipal "Scoop the Poop" initiative was credited with improving the water quality. In 2006, all but one sample of 6 met the water quality standard for fecal coliform. One thing that has changed since 2006 is the air temperature. This year we had record high temperatures and moderate drought conditions for much of the summer.

Another important chapter for the lake was the illegal introduction of northern pike in the early 2000s, which decimated the game fish population. The state began stocking the lake in 1982 with rainbow trout and salmon. Biologists stopped stocking in 2001 after pike were discovered. In an Alaska Department of Fish and Game report from 2008 entitled, Cheney Lake Restoration Project, the use of the chemical Rotenone to remove the pike was proposed. This after other efforts to remove the pike proved unsuccessful. An Anchorage Daily News article published on May 6, 2009, reported that after application of Rotenone, there was no evidence of any pike remaining in the lake. Stocking the lake resumed shortly thereafter.

To try to learn more about lake water quality, we collected water samples a few days after this observation was posted, from the beach area on the south side of Cheney Lake. The samples were sent to Dr. Dean Stockwell at the University of Alaska Fairbanks (UAF), Institute of Marine Science. Dr. Stockwell an algae expert, analyzed the water samples, made images of the microscope slides, and provided the following consult:

Dean Stockwell with the Institute of Marine Science at UAF writes:

The first picture is the blue-green algae. The water looked fairly clear. Usually blue-greens will bloom where there is excess nutrients. Being this late in the summer, your early phytoplankton bloom is over. I don't think it's a problem at the moment. There was concern about fecal coliforms from animals (primarily geese). I wouldn't drink the water there just knowing the history. A gravel pit that flooded, northern pike removed chemically, and problems with coliform bacteria. Also, blue-greens can produce toxins (another reason not to drink). I don't think it is a worry unless the water turns a milky green. Discoloration of the water is a sign of something blooming. If you see something like that, grab a bottle of water and keep it in a fridge until you can send (by the next day if you can).

Comments from LEO Editors:

According to the Municipality of Anchorage (MOA), there are only two lakes in the city that are "officially sanctioned for swimming," Goose Lake and Jewel Lake. For more information about Anchorage lakes, see the Lakes page at the MOA website. This post looks very similar to an observation posted by Mike in August of 2015 about algae in the lake on the ANTHC campus. At the time, we received a consult from Gino Graziano, Invasive Plant Instructor for the UAF Cooperative Extension Service. Gino wrote:

We have observed and received reports of excessive algae growth on lakes in the Anchorage area. There are two major types of algae, filamentous green algae and blue-green algae, which are actually a cyanobacteria. To tell the difference between these, try picking up a mat of the material. If you can pick up the algae masses, then it is a type of filamentous green algae. If you cannot pick up the algae than it is a type of blue-green algae. Large blooms of either of these algae are usually a sign of high nutrient levels, and I bet the warm weather and low water levels are helping. I have been to several non-urban lakes this summer, and not observed these algal blooms, so I suspect it is a combination of extra nitrogen from waterfowl, dogs, and other runoff sources that are causing the blooms in some urban water bodies. When these algae decay, they can deplete oxygen or cause undesirable odors. If they are cyanobacteria, some species can produce toxins in the water. I do not immediately see any non-indigenous or invasive species such as Elodea in the pictures, but since Elodea is a submerged aquatic, it may be right underneath some algae. Mike Brubaker