Printable Map - States with Chlorophyll Criteria
The map below shows a national summary of current numeric EPA-approved chlorophyll-a criteria. While total nitrogen and total phosphorus criteria are preferable for directly determining TMDLs and NPDES permit discharge limits, states may still use chlorophyll-a criteria as a means for determining whether waters are impaired due to nitrogen and phosphorus pollution. Chlorophyll-a is a response variable that measures biotic productivity and activity, thus reflecting the nutrient enrichment of the system. Chlorophyll-a concentrations are a direct response to causal variables - total nitrogen and total phosphorus. See Technical Support for Numeric Nutrient Criteria Development.