Study shows more than 77% of Southern California’s coastal stream kilometers contains trash

The Southern California Bight 2018 Regional Monitoring Program has published the findings of a regional survey of trash in aquatic environments that concluded that 77% of Southern California’s 4,600 miles of wadeable streams contain trash – with plastic being the most abundant type of trash.

The study, described in an article published in June by the journal Frontiers in Environmental Science, found that urbanized areas had about twice the amount of trash as natural areas. High road density and proximity to roads were two influential factors associated with high trash levels.

Researchers also found a significant decrease in the number of plastic bags in streams compared to a previous 2011-2013 stream trash survey; between the surveys, a 2016 statewide ban on single-use plastic bags went into effect. The study, which was done in partnership with the Southern California Stormwater Monitoring Coalition (SMC), concluded that such management actions are having a positive effect on reducing trash pollution.

The study data is expected to help develop mitigation strategies for reducing trash pollution in coastal watersheds and evaluate management successes.