Waste water treatment plants (WWTP) in Puerto Rico continuously discharge their effluents to streams, changing downstream chemistry and posing a risk to riverine and estuarine organisms. Impacts on receiving waters will vary depending on the nutrient load and hydrologic contribution made by WWTP effluents. Effluent discharges are regulated based on organic load contributed to receiving waters, and thus largely refractory organic matter should be found in WWTP effluents. Stream communities rely on organic matter and the type of organic matter in the stream can be altered by changes in the landscape or human activities (e.g. WWTP). This study evaluates three streams receiving effluents from WWTP (two secondary and one tertiary) and the effects of sewage effluents on stream metabolism. Measurements of diurnal dissolved oxygen are being taken upstream and downstream of the WWTP effluent using the two-station method. In addition, stream discharge, photosynthetically active radiation (PAR), algal biomass (chlorophyll a and ash free dry mass), FPOM and CPOM are being determined. Water samples are being collected and analyzed for stream phosphate, nitrate, ammonium, DON, and DOC flux.