Scientists at San Diego State University have successfully completed a study with a new early warning system to track the levels of untreated sewage in the Tijuana River. The team, led by SDSU biologist Trent Biggs and environmental engineer Natalie Mladenov, used specialized fluorescence sensors to detect and differentiate treated and untreated sewage where the river crosses the international border and in a creek of its estuary. “Our overall objective was to create a real-time sewage monitoring system,” Biggs told City News Service. “We had two main unknowns: What percentage of pollutants in the river are raw sewage with high bacteria levels — which is critical to monitor progress as new infrastructure is installed — and what happens to that sewage?”