After 10+ years of identifying high bacteria at certain places, the SLO Chapter Blue Water Task Force started using eDNA water quality source tracking in an attempt to help find the source of bacteria that can affect recreational water quality.
This report includes data collected between August 2024 and August 2025. Water and DNA samples were collected at four sites including Pismo Beach (Pismo Creek, Pismo Beach) and Avila (SLO Creek Mouth and Avila Pier). Enterococcus samples were likewise collectedfrom Bello Street bridge, Study sites were visited monthly and water samples collected for human eDNA (environmental DNA), Enterococcus, E. coli, and five additional species. Enterococcus concentrations were determined in house according to standard procedures.
DNA samples were sent to Jonah Ventures for qPCR analysis and identification of species. Pismo Creek had the highest numbers and most consistent occurrence of human eDNA, E.coli and Enterococcus. This is consistent with historical data for Enterococcus from this site. Enterococcus results indicate that levels were lower at Bello St. bridge on Pismo Creek 0.51miles upstream from the DNA collection site suggesting that a reservoir exists between these sites or that significant contamination input occurs between these sites. The results indicate that the water in Pismo Creek and Lagoon is not suitable for human contact. Pismo Beach ocean water had high occurrence of human eDNA and dog eDNA but bacterial levels were generally acceptable for human contact. San Luis Obispo Creek Mouth (SLO Creek Mouth) had consistently high levels of human eDNA, E. coli, and Enterococcus along with lower amounts of dog, poultry, and swine. The water at the mouth of SLO Creek is generally not suitable for human contact. Avila Beach had human eDNA in all samples collected along with four dates where Enterococcus levels were above safe contact values.