Global warming and pollution due to human activities has had a major impact on the world’s waterbodies which are vital for sustaining life on this planet. With this rapid escalation of threat to the oceans, seas, lakes, and rivers there has been an increased focus and urgency to monitor these changes to better understand the consequences of our anthropogenic impact. This culminates in a greater need for monitoring technologies to gather real-time data with high temporal and spatial resolutions to provide a holistic understanding of the changes to the waterbodies and inform regulations to protect our waters from further damage. The bridge the technological and research gaps required to sufficiently monitor the aquatic environments the work presented in this thesis aimed to demonstrate the design and development of beyond state of the art in situ optical detection by applying advanced optical and electronic components. A unique and novel design was produced by applying two mini spectrometers, a multispectral LED array light source, a photodiode, and custom electronics for interfacing with the optical system and housing the system in a robust enclosure using advanced manufacturing methods. The finalised system and enclosure design was replicated by manufacturing multiple identical systems as low-cost going beyond what is currently being achieved in the research field. The systems were demonstrated to have superior multispectral and multiparameter optical measurement capabilities when compared to current commercial systems with higher resolution detection of chlorophyll and turbidity as well as the ability to measure other tested analytes of petroleum and dissolved organic matter. The built systems showed robustness through repeated deployments and provided insightful data on the locations of deployment measuring multiple different environmental events while in situ.