Hope you are enjoying the sunny weather lately. Despite the cold nights it is a nice break from the cloudy and rainy December and early January. So far this water year (Oct. 1-Sept. 31) the lake has received 25 inches of rain, which is only about 10 inches below the annual average and eight months to go. According to the Oregon Department of Agriculture it is supposed to be drier through February, but wet again in March and April. This will be good for the mountains and can hopefully prolong the snowpack. It will also be good for the lake to have a wet spring and early summer as it delays when we open the headgate.
The lake has cleared somewhat, with water clarity to the bottom in Lakewood Bay, nearly to the bottom in West Bay, and to just over five feet in the Main Lake. Visibility in Main Lake on January 4 was over eight feet before heavy rain later in the week. It rained two inches the day Lara was out sampling and continued to rain for the next four days for a total of 4.25 inches for the five-day period.
Water temperature this summer reached a high of 81 degrees at the end of June after three days of triple digit temperatures. Phosphorus in the lake was higher than it had been since 2018 so the temperature and nutrients favored cyanobacteria. We had cyanobacteria well into January this winter but it looks like it is mostly gone by now.
Cyanobacteria are less tolerant of cold weather and this time of year other algal species are competing with them for nutrients. Currently the lake is dominated by diatoms, which will persist until water starts to warm again in late spring. Diatoms are a very beneficial species that are an important component of the food chain, containing long-chain fatty acids that feed zooplankton, aquatic insects, and fish.
This coming year we continue to focus on phosphorus reduction, starting with an updated system to treat incoming river water. As previously mentioned, the longer we hold off using the river the better we are, so if we do have a wet spring and early summer that will really help. Once the headgate is open we will dramatically increase our alum injection to intercept phosphorus before it gets to the lake.
There is nothing we can do about the temperature, but our second year of La Niña weather pattern may lead to cooler air temperatures this summer. That was the case during summer 2018 when there were 35 days of air temperature above 90 degrees, followed by only 10 days in 2019. However, 2018 was the end of La Niña and 2019 was the start of El Niño so it is difficult to make inferences from a single data point.
Anyway, let’s hope for a cooler summer nonetheless.