Launch the map to explore the water quality of the nine swimming sites targeted by the SGRRMP during the summer of 2019. By clicking on a site you will see a pie chart that shows the proportion of times that water samples had FIB concentrations that exceeded the regulatory thresholds below. These thresholds are based on the risk of becoming ill when FIB concentrations reach these levels.


Up until 2007, little was known about the risk of becoming sick for people who swam in the streams and rivers of the San Gabriel River watershed despite the fact that thousands of people swim in these waters during the summer months. As a result, the SGRRMP bacteria monitoring program was established with weekly water sampling for fecal indicator (FIB) bacteria during the summer months (May to September) at high use recreational swimming areas.

Since 2007 it was learned that the majority of water samples collected on or near weekends and holidays had the highest concentrations of FIBs. This is associated with increased numbers of people that are swimming.

Below are the regulatory thresholds for E. coli. When concentrations exceed these standards, there is a human health risk for swimming.

Fecal Indicator Bacteria	Single Sample	30 Day Geometric Mean
E. coli	235 MPN/100 mL	126 MPN/100 mL

The 30-day geometric mean standard is based on a set of 5 samples collected within a 30-day period. When the geometric mean is elevated it indicates that there have been persistently elevated bacteria concentrations.