An autonomous microfluidic sensor for phosphate in environmental waters has been developed and validated in laboratory and field trials. The sensor is based on the molybdenum yellow method for phosphate detection and employs a microfluidic manifold where mixing, reaction and detection take place. Optical detection is performed using a light emitting diode (LED) light source and a photodiode detector, while wireless communications allow near real-time access to the collected data. In parallel with this work, detection schemes for other nutrients (ammonia, nitrate/nitrite) are being developed, with the goal of developing a low cost, field deployable multi-nutrient detection platform. Utilising colorimetric chemistry and LED-based detection systems allows a modular approach which facilitates integration of new detection schemes with the platform provided by the phosphate sensor. The multi-nutrient analyser system will benefit a range of users including local authorities, monitoring agencies and the municipal and industrial wastewater treatment sectors.