Coastal waters buffer catchment and oceanic fluxes, and house important environmental assets that support marine protected areas, recreation, fishing and industry. Merchant vessels plying regular coastal routes provide an “opportunity” to monitor water quality of coastal waters. Onboard sensors can monitor at relatively low cost and effort, compared to traditional approaches. While common overseas, such vessels of opportunity are an untapped resource in Australia for observing our coastal waters. Deakin University recently re-instated water quality monitoring on the 194m Spirit of Tasmania 1 ferry, with daily transects across Bass Strait from Geelong to Devonport. This was duplicated on the 12m Gippsland TAFE vessel, Bar-ba-ka, to provide regular water quality sampling through Gippsland Lakes and offshore. Regardless of scale, the data provides a pseudo spatial-temporal integration of system dynamics that can advance the interpretations from spatially-limited or temporally-limited monitoring. This paper compares traditional sampling, with insights from autonomous vessel monitoring using local examples, and mature programs overseas. It also considers effort and cost to indicate the relative efficiency of this data collection method. We suggest the fleet of coastal vessels run by state agencies, institutes and private operators could be integrated into a broader monitoring network, to meet future monitoring needs.