Los Angeles City Sanitation staff sample and test water twice a week at three locations in each of the Los Angeles River Recreation Zones, corresponding to the beginning, middle, and end of each zone. Samples are tested in a laboratory for the presence of E. colibacteria, and for each sample a resulting MPN (Most Probable Number) per 100 milliliters (mL) is determined. The bacteria results at each location are compared to State of California water quality standards for water contact recreation (REC-1 and Limited REC-1) to determine if the water quality, in each Recreation Zone, is suitable for recreational activities.

You can goo to http://lacitysan.org/lariverquality to check the latest water quality status of the rec zones.

Based on the bacteria levels found, the status of each recreation zone is determined and displayed on the table below according to the following colorcode:

Color Code Description
GREEN - OPEN Water quality is suitable for recreational activities, but swimming in the river is still prohibited. Test results indicate bacteria levels lower than 235 MPN, the limit for REC-1.
YELLOW - CAUTION Users should exercise increased caution. Test results indicate bacteria levels between 235 MPN (REC-1) and 576 (Limited REC 1) at one or more of the sampling sites located in the recreation zone or above 576 at only one of the sites.
RED - CLOSED This LA River Recreation Zone is not suitable for recreational activities. Test results indicate levels exceeding 576 MPN (Limited REC-1) at two or more of the sampling sites located in the recreation zone. A Closure Advisory will be issued by the City of Los Angeles and the MRCA will close the recreation zone and post closed signs. The recreation zone will stay closed until further bacteria testing show that the zone is once again suitable for recreational activities.