Remediation of Pesticides in Oso Flaco Creek

Taking core samples of the sediment

April 2021 Initial Study/MND Remediation of Pesticides in Oso Flaco Creek

This Initial Study, completed in April 2021, provides a preliminary analysis of the proposed Remediation of Pesticides in Oso Flaco Creek’ project. The study determines what type of environmental review will be required and allows for modification of the project to mitigate adverse impacts. Read the Study.

Coastal San Luis Resource Conservation District (CSLRCD) has worked with public and private landowners and resource management agencies to protect and remediate agricultural land and aquatic systems in the Oso Flaco watershed since 2000. This watershed is characterised by low gradients, highly erosive sandy soils, year-round intensive agricultural production and some of the highest concentrations of legacy pesticides, particularly DDT, in the state.

Oso Flaco Lake

In 2018, CSLRCD was awarded the Remediation of Pesticides in Oso Flaco Watershed project, funded by the State Water Resource Control Board (SWRCB). Based on numerous studies, assessments and planning efforts undertaken by CSLRCD and partners over the past 20 years, the project proposes to remove and remediate sediment from 1.2 miles of Oso Flaco Creek where high concentrations of DDT persist. Excavated sediment is to be remediated on site, deploying a multi-layer remediation process that results in levels of DDT below thresholds protective of aquatic habitats and human health.

In addition to sediment excavation and remediation, the project implements a series of Best Management Practices (BMPs) in the upper watershed to prevent continued erosion of topsoil into the waterways. Planned BMPs include resizing an undersized culvert, considered one of the primary contributors of sediment mobilization in the watershed; a sediment basin designed to filter out fine sediments from agricultural tailwater; and technical assistance and consultation provided to reduce use and increase efficiency in irrigation water usage.

This project is part of a multi-phased remediation process and brings together a broad range of local partners, including private and public landowners, special interests groups and resource management agencies.

CSLRCD staff are currently developing design plans and securing permits for the project, which is anticipated to go to construction in 2022 or 2023.


CA Dept. of Parks & Recreation, Oceano Dunes District

CA Dept. of Pesticide Regulation

Teixeira Farms

County of San Luis Obispo


CA State Water Resources Control Board

RCD Contact:

Hallie Richard,