San Gabriel River Regional Monitoring Program
The CSCI was calibrated during its development so that the mean score of reference sites is 1. Scores can range from 0, indicating altered biological condition to > 1. In practice, CSCI scores observed from nearly 2000 study reaches sampled across California range from about 0.1 to 1.4. The four categories presented above were based on the 30th; 10th; and 1st percentiles of CSCI scores at reference sites. While these ranges do not represent regulatory thresholds, they provide a useful method for interpreting CSCI results.


  1. Mazor, R.D., A. Rehn, P. R. Ode, M. Engeln, K. Schiff, E. Stein, D. Gillett, D. Herbst, C.P. Hawkins. 2016. Bioassessment in complex environments: designing an index for consistent meaning in different settings. Freshwater Science, before publication.
  2. Rehn, A.C.,R.D. Mazor, P.R. Ode, 2015. The California Stream Condition Indices (CSCI): A New Statewide Biological Scoring Tool for Assessing the Health of Freshwater Streams. SWAMP Technical Memorandum. SWAMP-TM-2015-0002.

The overall condition of streams in the San Gabriel River Watershed has been assessed by collecting benthic macroinvertebrates (BMIs) and attached algae during dry weather conditions in the spring and summer at over a hundred stations since 2008. BMI communities provide an integrated view of stream water quality over time since their juvenile forms spend most of their lives living on the stream bottom or water column. The attached algae community includes both diatoms and soft algae whose populations change rapidly in response to changes in water quality. The biotic condition for BMI populations at each site was determined using the California Stream Condition Index (CSCI) and for attached algae the Southern California Algae IBI (SoCA IBI). The SoCA IBI is in the process of being replaced by the Algal Stream Condition Index (ASCI) which will be presented here in 2021.

The California Stream Condition Index (CSCI) is a statewide biological scoring tool that translates complex data about benthic macroinvertebrates (BMIs) found living in a stream into an overall measure of stream health. The CSCI combines two separate types of indices, each of which provides unique information about the biological condition at a stream: a multi-metric index (MMI) that measures ecological structure and function, and an observed-to-expected (O/E) index that measures taxonomic completeness. Unlike previous MMI or O/E indices that were applicable only on a regional basis or under-represented large portions of the state, the CSCI was built with a statewide dataset (n = 1,985 sites) that represents the broad range of environmental conditions across California.

On the map to the left you can explore the biological condition of each region of the San Gabriel watershed by viewing pie charts that depict the proportion of stream reaches that were found to be in one of the following condition categories

  1. ≤ 0.62 Very Likely Altered
  2. 0.63 to 0.79 Possibly Altered
  3. 0.80 to 0.92 Possibly Intact
  4. 0.93 to ≥1.0 Likely Intact

Stream Classification and Prioritization Evaluator (SCaPE)

In 2018 a statewide landscape model was developed by the Southern California Coastal Water Research Project (SCCWRP) that predicted the ranges of likely scores for the macroinvertebrate-based bioassessment index (CSCI) within landscape constraints to prioritize management actions. The model provides a context for what is likely to be observed at a given site independent of an actual bioassessment score. With this approach, sites can be described as over- or under-scoring relative to an expectation that is typical for the observed level of landscape alteration. Go to SCaPE to find more information.