Summer Alum Treatment

Water Quality - 8/12/2022
Summer came on in a hurry this year and the lake is getting a bit green as a result. We usually end up with a green lake this time of year but we were optimistic the wet spring would lead to good conditions all summer. However, when you have a week of 90-100 degree weather it erases any gains from the late spring. The weather is going to get warm again next week so no relief is in sight.

Even though the average monthly water temperature for May and June was on the low side historically, that shifted dramatically by the end of July. The water temperature peaked at 82 degrees on August 2, following the week of hot weather. The water has cooled a few degrees since the peak, and the days are shorter so the lake will continue to cool into fall. If you want to reach cool water now you will have to dive down about 20 feet where the water is closer to 65 degrees.

Our goal during summer is to keep phosphorus levels in the lake as low as possible. This means limiting the amount of Tualatin River water we use to keep the lake full since phosphorus in the river is five times what we want in the lake. Last year we installed a pump-back system to capture water that leaks through a spring near our powerhouse. The pump was designed to capture the approximately 1.5 million gallons per day that leak out and send it back up the flume line into the lake. That worked well last year to delay when we opened the headgate but the pump motor failed this spring so we have not been able to use it. The motor has been replaced and should be operational by the time you read this. The result of not capturing this water means we are relying more on the river to keep the lake full. With the pump operating again we will be able to reduce our reliance on the river.

We also installed an enhanced alum treatment system near the headgate to remove phosphorus from river water we bring in. That is operational now and we are adjusting the air and alum flow to maximize phosphorus removal. It will not remove all the phosphorus, but the goal is to capture the soluble portion that is immediately available to feed algae. 

Speaking of alum, we have scheduled a surface application for the week of August 22. This will strip cyanobacteria and nutrients from the lake and should give us good water quality for the rest of the summer. If you have not witnessed this process before but have attended our pup-up concerts, you have seen the barge we use to apply alum. We convert the barge from its entertainment role to a treatment system and push it back and forth across the lake applying alum. There is no danger from the treatment, and you can continue to use the lake during the process, but PLEASE stay away from the barge so the crew can concentrate on steering the barge along the designated path. Also, do not make large wakes around the barge since they toss it around and make it difficult to steer.



Treating the lake will remove much of the cyanobacteria currently growing in the lake, but we want to assure you the lake is still safe to use with a certain level of cyanobacteria present. Our goal is to not let the concentration get high enough to pose a health threat, but there may be isolated areas where cyanobacteria have floated to the surface, and wind concentrates the colonies around the shoreline. If it gets to that point before our treatment you can continue to use the lake, just avoid the areas with surface concentrations.

Stay save and have a great August!