Algae Clogging Water Treatment Filters? A DSPUD Case Study

Project summary

The Donner Summit Public Utility District (DSPUD) supplies drinking water from Lake Angela, an 18-acre reservoir in California’s Sierra Nevada. For years, recurring blooms meant algae clogging water treatment filters every summer. As a result, chemical dosing climbed, and filter cleaning consumed millions of gallons of finished water. In 2025, a single MPC-Buoy changed that pattern. During its first season, plant-cleaning water use dropped 45%. Influent turbidity fell 67%. Moreover, the District saved roughly $86,000 on water alone. Consequently, the Board extended the program for two more years in November 2025.

The challenge: algae clogging filters, rising costs

Algal blooms are part of Lake Angela’s history. Significant events occurred in 2009, 2015, 2016, 2022, and 2024. Sampling showed green algae such as Chlorella sp. and Oocystis sp., together with the diatoms Navicula, Cocconeis, and Cyclotella. In other words, a mixed algal community — and one that strained the treatment plant downstream.

Each summer, rising cell counts moved through the plant in sequence. First, filters blinded faster. Next, clarifiers ran near their limits. Meanwhile, operators raised chemical dosing to break down the incoming algae. Killing the cells created a new burden, however. The residue built up in the process. Therefore, crews backwashed filters and flushed clarifiers far more often, and every cycle consumed finished water.

“When the algae in the lake got out of control, we had little choice but to add large amounts of chemicals to kill them. Unfortunately, the dead algae then clogged the system and forced us to flush everything out.”

— Steven Palmer, PE, CSDM, General Manager, DSPUD

Weighing the alternatives

Before choosing ultrasound, the District weighed its alternatives. Dosing the reservoir itself with algaecides came up first. However, the Board set that idea aside early — “we wanted to avoid that, just from an environmental point of view,” Palmer said. The team also evaluated a coagulation-based pre-treatment stage. That route required a pilot study first, which meant more budget and more waiting. Instead, DSPUD wanted proof within a single bloom season, at a defensible cost.

“The buoy just seemed like a simple, straightforward, elegant solution.”

— Cathy Preis, President, Board of Directors, DSPUD