Dear friends,
Restore the Delta’s Delta Science Program officially wrapped up its summer water quality monitoring at the end of September. Since 2022, our water quality monitoring program includes:
- Recording water temperatures and weather conditions
- Testing for harmful algal blooms (HABs)
- Assessing salinity levels
New this year, in collaboration with the Central Valley Regional Water Quality Control Board (Region 5 of the State Water Board), we added E. coli collection and sampling to our regular monitoring routine. With the introduction of golden mussels into the Delta via Rough and Ready Island and the added E. coli sampling, we have a few new topics to cover, and we want to help break them down.
1. First off, let’s talk about HABs and what our monitoring teams observed in the field.
A bit of positive news for the community: We didn’t see much bloom activity at all this summer; otherwise, you would’ve heard from us earlier this summer through social media to exercise caution while recreating. While there were small traces of blooms, which looked like small flakes in the water at Buckley Cove in Stockton, the blooms posed no threat to recreation due to the low quantities and lack of toxin concern. The lack of HABs may have come as a surprise to many, given that we experienced very hot periods this summer, and HABs thrive in warm water. However, California did experience a wet water year, which kept consistent flows in the San Joaquin River during the hottest periods, according to the few flow monitors near Stockton on the California Data Exchange Center (CDEC). We hope to see this trend continue, but there are concerns with the introduction of golden mussels and a potential interaction with HABs proliferation.
2. Golden mussels were first detected in the Delta in October of 2024 at Rough and Ready Island, near Stockton; learn more about them from the California Department of Fish and Wildlife here.
Within the 2 years that golden mussels were introduced into the Delta, they have spread across California’s water system, with potential to impact drinking water systems across the state. In the field this year, our team observed that the waterways are very clear, so much so that our team was able to see the bottom of the water bodies clearly, which we haven’t been able to do before. What might this have to do with golden mussels? Well, golden mussels are filter feeders, and they have been spotted in large clusters around a majority of the sites that RTD’s monitoring team has been sampling. Although filtering can seem like a great thing because clear water must mean the water is clean, that’s not necessarily the case. One problem is that as golden mussels filter, they release nutrients like phosphorus and nitrogen, which HABs thrive on (Zhang et al. 2024). There’s also the concern of how this clearer water may affect wildlife species within the different water columns – a certain level of turbidity is important for species survival. Golden mussels are a problem that we don’t fully understand yet, which is why we are glad that Assembly Member Rhodesia Ransom was able to secure 6 million dollars for management and response from State Water agencies.
3. Sampling E. coli levels throughout the Delta this summer.
Overall, much of Stockton fell below the recreational E. coli threshold, but throughout different times of the season, two sites became areas of concern. For one week in June, the Mormon Slough had levels that tripled the recreational-concern threshold of 320 MPN (MPN, the most probable number, is a measure for E. coli). The main concern we saw was at the end of Yosemite Lake on the Smith Canal, at American Legion Park, where many people fish. The E. coli levels were at their worst, recorded at 8 times the 320 MPN threshold at one point. These levels eventually declined to 2-4 times the threshold in May through July. The levels continued to fluctuate, dropping below recreational levels before spiking to 8 times the threshold again in mid-September. These numbers were a cause for concern, especially for those fishing at American Legion Park and pets that roam the surrounding neighborhood.
Our team would like to acknowledge that this work does not get done without the support we receive. The collaboration with the Central Valley Regional Water Quality Control Board on both the HABs and E. coli testing supplies was pivotal in helping us to maintain our testing.
We also couldn’t have gotten this work done without the help of our Climate Water Advocates, who quickly adapted to the new monitoring procedures. Although Summer has come to an end, we hope to continue addressing water quality issues with our monitoring programs and to keep our Delta communities informed.
- View this testing season’s recorded E. coli data here.
- Stay up to date with statewide HABs reporting, including the data we have collected, available here.
References:
Zhang, J., Xu, M., & Yang, Y. (2024). Assessing the effects of environmental factors on filtration rate of golden mussel (Limnoperna fortunei). Ecological Indicators, 158, 111544. https://doi.org/10.1016/j.