By Bruce Houdesheldt
Despite the prevailing dry conditions in warmer months, the Sacramento Valley and the north Delta have remained free of harmful algal bloom (HAB) detections—a testament to our proactive monitoring and mitigation efforts. As we continue to closely watch over these waterways and utilize the latest technology, we’re committed to keeping our communities safe and our ecosystems thriving.
With warmer temperatures and summer recreation at California freshwater lakes and rivers on the horizon, it is time for Californians to be vigilant about the dangers posed by freshwater Harmful Algal Blooms (HABs). According to the California Department of Water Resources (DRW), algal blooms can release toxins into the water which have the potential to significantly harm both people and pets. It can also create hypoxia which impacts fish populations.
In response to increasing detections of harmful algal blooms due to dry conditions and climate change, legislation was passed in 2019 which authorized the development of a Harmful Algal Blooms (HABs) Portal by the State Water Resources Control Board and the California Water Quality Monitoring Council. A HAB Incidents Map, is maintained and updated weekly by the State Water Board, which shows locations where HABs have been reported.
In November 2022 the Delta Stewardship Council Delta Science Program released its Delta Harmful Algal Bloom Monitoring Strategy A Working Document to Develop a Community Monitoring Strategy. Management questions in the Strategy support the implementation of Assembly Bill (AB) 834 to protect water quality and public health from HABs and the Water Resilience Portfolio Action 8.1 that calls for implementation of AB 834.
The Strategy recognizes there are many drivers and impacts of HABs (see Kudela et al., in press), and the importance of research in understanding HABs impacts on communities and calls for future work beyond the 3–5-year horizon of the strategy that addresses these knowledge gaps after initial coordinated HABs monitoring has been established.
Part of that research and monitoring is in included in the Delta Regional Monitoring Program the FY 24-25 Monitoring Workplan which asks the question “What are the thresholds for nutrients (nitrogen (N) and phosphorus (P) and their ratios) that can limit Harmful Algal Bloom (HAB) biomass and cyanotoxin accumulation to safe levels, limit the abundance and distribution of nuisance macrophytes, and support robust growth of desirable phytoplankton and macrophytes throughout the Delta?”
HABs and their associated toxins are increasingly a problem in the Delta and are expected to become more prevalent with climate change impacts fueling the conditions (e.g., low water flow, increased water temperatures) that lead to blooms. Toxins from HABs can harm aquatic life and humans and impact the water bodies California relies on for industry, drinking water, and recreational purposes.
Another tool in the toolkit is California-Harmful Algal Risk Mapping (C-HARM) Model which generates predictions of harmful algal bloom (HAB) conditions through a combination of 1) sophisticated circulation models that predict the ocean physics, 2) satellite remote-sensing data of the ocean “color” and chlorophyll patterns, and 3) statistical models for predicting bloom and toxin likelihoods.
