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We describe a collaborative effort to develop and implement a new integrated water quality monitoring package that provides continuous and simultaneous multi-parameter physical and biogeochemical measurements, including: conductivity, temperature, pressure, dissolved oxygen, chlorophyll fluorescence, and turbidity. The "water quality monitor" (WQM) features autonomous operation and multiple anti-fouling approaches, and is intended for long-term deployments (months) in potentially high-fouling coastal environments. Our primary objectives for our in-field tests are 1) to collect high quality data for >3 months without the need for instrument service, 2) to present results from field trials in coastal regimes in order to assess the WQM's longevity and efficacy of multiple antifoulant approaches, and 3) to demonstrate that the WQM as a single, multi-sensor instrument provides reliable, multiparameter data in a single data stream, simplifying data analysis and management for ocean observing system integrators. Results from preliminary performance testing of the WQM deployed in Chesapeake Bay, MD, from April 20, 2006 to July 3, 2006 showed negative effects of biofouling within 2 months. Lessons learned from this deployment helped evolve the instrument design and highlighted the need for more aggressive measures to deter the effect of biofouling. To determine the best approach to further reduce the effect of biofouling over the deployment period in addition to copper guards, WQMs were deployed with sea-bird anti-foulant cartridges (AF) only, WET Labs bleach injection system (BLIS) only, or a combination of AF and BLIS. A total of 5 prototype WQMs were deployed in two separate coastal environments. Sea-bird electronics conducted tests at Shilshole Marina, WA continuously for 5 months straddling the end of the summer growing season, fall and winter months (August 15, 2006 to January 15, 2007). WET Labs conducted tests in Yaquina Bay, OR for just over 4 months during sim- ilar growth conditions (September 13, 2006 to January 23, 2007). Since the deployment period extended from late summer to winter, biofouling conditions were considered to be moderate. Results show temperature, salinity, dissolved oxygen, turbidity and chlorophyll fluorescence values were highly coherent among multiple instruments over 4 and 5 month deployment durations. WQMs equipped with either the AF or combination of AF + BLIS recorded high quality data for 110-152 days (>3-5 months). Of particular importance was the stability of the dissolved oxygen measurements which showed less than 5% signal degradation over the deployment period. In-field validation measurements of dissolved oxygen were made with a calibrated reference SBE43 dissolved oxygen sensor and with discrete water samples for Winkler analysis. Temperature and salinity were very stable based on pre and post-deployment calibrations and drift was <0.001 degrees C and 0.006 psu, respectively. Designed specifically to address the ocean and estuarine observing needs, the WQM provides a reliable, cost effective, research-grade water quality monitoring solution for long-term deployments without need for frequent instrument service.