Using predicted chlorophyll-a and cyanobacteria concentrations in surface waters to characterize harmful algal bloom impacts on US drinking water quality

The first part of the presentation describes how EPA's national nutrient inventory, StreamCat, National Lake Assessment, and other datasets were used to predict chlorophyll-a and cyanobacteria abundance across the conterminous U.S.  The second part of the presentation shows how the chlorophyll-a and cyanobacteria predictions were associated with drinking water data from EPA's Safe Drinking Water Information System (SDWIS) to calculate where drinking water systems are most at risk from harmful algal blooms (HABs) in their source waters. Risk was calculated using a weighted summation approach with data on lake risk (lake morphology, chl-a, temperature, nutrients, etc.), drinking water system risk (treatment technology, deficiencies, etc.), and exposure risk (population served, health-based violations, etc.). Risk for HABs were generally found to be in areas with high agricultural nutrient inputs. This risk analysis can help determine potential sources of risk and be used for prioritizing locations and public water systems that may need further resources to protect human health.

Impact/Purpose

This is a presentation that will be given by Meredith Brehob and Michael Pennino at the HABs, Hypoxia, and Nutrients Research Webinar Series on September 24, 2025.  The audience is both inside and outside the EPA.  The goal of the presentation is to show how predictions of harmful algal blooms (HABs) in lakes that are used as source water for public drinking water systems may pose risk to human health.  The analysis combines data from the national lake assessment, EPA's national nutrient inventory, StreamCat, and the Safe Drinking Water information system and other sources.  The results of this analysis may be able to help determine potential sources of risk and be used for prioritizing locations and public water systems that may need further resources to protect human health due to HABs in source waters. 

Citation

Brehob, M., M. Pennino, AND R. Sabo. Using predicted chlorophyll-a and cyanobacteria concentrations in surface waters to characterize harmful algal bloom impacts on US drinking water quality. Harmful Algal Blooms, Hypoxia, and Nutrients: Research Webinar Series, Washington, DC, September 24, 2025.