Aquatic toxicity tests provide another measure of potential impact; however, unlike ecological monitoring, water column laboratory bioassay tests do not incorporate aggregate impacts associated with habitat condition and effects associated with sediment exposure. However, aquatic toxicity tests can furnish a more direct measure of potential impacts from chemical contaminants, particularly those not specifically measured.

From 2008 to 2014, 71 toxicity tests were conducted using the water flea, Ceriodaphnia dubia, survival and reproduction test. Seven day exposures to undiluted field collected stream water were conducted. The results of the reproduction endpoint (chronic toxicity as young per female) is presented here since it was far more sensitive compared to the survival endpoint.

Toxicity testing was dropped by the Technical Steering Group following the 2016 sampling season due to low and sporadic toxicity.

On the map to the left you can explore the proportion of water samples that exceeded the toxicity categories presented below, for each region of the San Gabriel watershed.