Daphnia: also known as water fleas, are tiny crustaceans that live in freshwater like lakes, streams and ponds but we see them more in clarifiers and are typically a good sign, indicating a well-functioning treatment process. Their presence suggests a healthy, clear water environment with low suspended solids, which is a desirable outcome in a clarifier. But they can disrupt EFF TSS testing by interfering with settling and increasing suspended solids.