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Nantucket Sound(Figure 16, outer station) for almost the entire flooding tide. For this reason, the final areas of eelgrass habitat or high quality benthic animal habitat in a eutrophying estuary are typically found within the region of the tidal inlet. The Health Index, as a composite of all major nutrient related water quality parameters, also allows for a tracking of temporal trends in water quality. Given the natural variation in water quality associated metrics, it is difficult to determine small short term changes. This is particularly true if changes result fiom a number of small and/or dispersed improvements in tidal flushing, nitrogen source reductions, etc. However, with the growing dataset it is now possible to examine if change is occurring within these estuaries (improving/declining). To this end,the Index data from Waquoit Bay from 2010-12;2013-14 and 2015-16 were compared to the historical baseline (Figure 15)with a similar analysis for Popponesset Bay(Figure 17). These comparisons are now sufficiently robust to show trends in estuarine health based on the integrated Index at the different sites between years. Values falling above the 1:1 line show an improvement, values below the line indicate a decline and values near or on the line suggests, no change at that site in that year from historical conditions. In Waquoit Bay it now appears that there has been a general improvement in regions of significant impairment(Index<30), small recent improvements in the moderately impaired areas fiom 2013-2016 and no change (I site)to a worsening of water quality(1 site) in the highest quality sites (>60). It should be noted that the declines seen in the 2015-2016 data are driven significantly by the large phytoplankton bloom in 2016. The importance of this event will depend on if it was a rare event spawned by low flows due to the 2016 drought or if it is part of a trend toward increasing bloom frequency and duration due to continued nitrogen enrichment. At this time there does not appear to be any major decline in water quality throughout the Waquoit.-Bay System. In comparison,water quality in the Popponesset Bay System showed more stability between years than Waquoit Bay,with the only clear result being the small improvement in the poorest quality areas (long term index<30). However, Popponesset Bay also had a moderately large phytoplankton bloom in 2016,which impacted water quality. Overall,the trend of improving water quality in the poorest quality areas is a positive sign for both estuaries,as these areas are most nitrogen enriched. Analysis of macroalgal accumulations in these areas may give insight into if the improvement is related to loading or a diversion to different primary producer(macroalgae versus phytoplankton. The above approach yields more information on change than the color coded mapping of results (Figures 14 and 16) which are based on single years and Index ranges. The direct comparisons are based on individual sites for individual years compared to the baseline conditions. This comparison indicates that for Waquoit Bay(Figure 15), the intermediate areas of impairment in the lower main basins tended to show poorer water quality in 2016, consistent with the observed higher chlorophyll-a (bloom) and oxygen depletions. Popponesset Bay showed a similar pattern (Figure 17) of slightly lower water quality in the main basin in 2016 compared to historical levels and experienced a moderately large phytoplankton bloom (which also occurred in Three Bays)with associated bottom water oxygen depletions. A single year is not a trend and more analysis is needed to determine the importance of the 2016 regional phytoplankton bloom to the restoration plan for these estuaries and if it is the result of a"rare" set of weather conditions or if it will become the new normal in response to continuing high levels of nitrogen enrichment. 20