Attachment 4.a. GiantKelpVariance

San Diego Regional Water Quality Control Board
September 11, 2026
Emily Allen
Area Operations Manager
United States Section
International Boundary and Water Commission
2995 Clearwater Way
San Diego, CA 92154
[email protected]
Subject: Most Sensitive Species for Whole Effluent Toxicity Testing Dear Emily Allen,
The San Diego Water Board acknowledges the ongoing constraints in obtaining giant kelp (Macrocystis pyrifera) for use in required chronic whole effluent toxicity (WET) testing. In response to USIBWC’s request, the San Diego Water Board is granting a conditional variance allowing the use of the purple sea urchin for chronic WET testing of SBIWTP effluent, when giant kelp cannot be obtained despite reasonable efforts. Summary of Giant Kelp Supply Constraints
In April 2025, USIBWC first reached out to the San Diego Water Board regarding challenges in obtaining a reliable supply of giant kelp for chronic WET testing of effluent from the SBIWTP. Nautilus Environmental and Bio-Analytical Laboratories, subcontractors for USIBWC’s contracted operator Veolia, described alleged restrictions imposed by the California Department of Fish and Wildlife (CDFW) on scientific collection permits (SCP) for giant kelp off the coast of San Diego. These alleged restrictions resulted in a significantly reduced take of giant kelp, making it difficult to consistently obtain enough giant kelp for weekly testing as required by USIBWC’s NPDES permit. Nautilus Environmental and Bio-Analytical Laboratories recommended that USIBWC request a variance from the most sensitive species requirement, allowing for the use of the second most sensitive species, the purple sea urchin (Strongylocentrotus purpuratus), to satisfy this weekly monitoring requirement.

Emily Allen, USIBWC

September 11, 2026

To corroborate this claim, San Diego Water Board staff met with the relevant staff from CDFW who explained that the SCP in question authorized a take of 50 sporophyll blades over the 3-year permit term, and the allowable take was routinely exceeded. A new SCP has since been issued, authorizing a take of 80 sporophyll blades per 3-year permit cycle. CDFW staff explained that the allowable take in the applicable SCP was not actually reduced, but it would be enforced moving forward. Additionally, CDFW staff noted that they may consider amending the new SCP to increase the take of sporophyll blades if the SCP holder identifies additional sites for sporophyll harvesting.