Water Quality Index Score: 82, Good

The San Luis Rey watershed, the northernmost watershed on our list, is dominated by the San Luis Rey River whose headwaters begin near Warner Springs and Ranchita. The watershed also includes parts of Valley Center, Bonsall, Fallbrook, and Oceanside. In 2016, San Luis Rey held the distinction of being the only watershed where the fecal indicator bacteria counts in all collected samples fell within the objectives for good water quality. Nutrient scores – particularly ammonia – were occasionally high though. Ammonia doesn’t usually stick around in aquatic systems very long as it is fairly quickly converted into nitrate, and so high level of this indicator can be a sign of industrial or fertilizer waste.

How to read our water quality pie charts:  these handy charts are designed to give you a sense of which of the factors we measured contributed to the overall water quality score (the number in the center) for each watershed. The size/color of the pie slice gets larger/warmer with increased frequency and magnitude of deviations from good water quality standards for each indicator.