A water toxicity detection system and method employ bivalve organisms as biological indicators to monitor aquatic environments in real-time. The system includes sensors configured to measure gape behavior of multiple bivalve organisms, generating corresponding gape measurements that are processed by a computing system. The processor normalizes gape measurements and calculates exponentially weighted moving average (EWMA) and exponentially weighted moving variance (EWMV) values to assess short-term behavioral patterns. A detection module uses EWMA and EWMV as state-space variables to identify deviations indicative of exposure to toxic substances, specifically detecting gape closing (GC) events characterized by increased activity followed by shell closure. The system generates system-level alarms when a predetermined fraction of individual bivalves simultaneously exhibits abnormal behavior patterns consistent with toxicity exposure. The technology enables early detection of waterborne contaminants including heavy metals, organic compounds, industrial chemicals, and algal toxins.