Biologically relevant macronutrients, nitrate + nitrite, silicate, phosphate and ammonia, were measured at all sites throughout the study. Nitrate + nitrite values (NOx) at the surface showed clear seasonal trends, peaking over winter and drawing down to near zero in summer and autumn. Phosphate concentrations also reached a peak in winter, which was associated with Southern Ocean influence. Median ammonium concentrations at all sites were generally <0.5 μM, with no clear peaks in any season or month. Overall, the lowest values were measured in August and other months showed reasonable spread around the median. Median silicate concentrations were consistently highest at sites 1 and 9, followed by site 5. Water from the River Derwent flows through site 1, then tracks east towards site 9 then site 5. Seasonally, silicate was generally highest in winter when the River Derwent outflow is also greatest.

Indicators of estuarine ecosystem health – temperature, salinity, turbidity, dissolved oxygen, chlorophyll a, pH, nutrients - were sampled each month for twelve months at four sites in Georges Bay and at the bridge at the river mouth by the Tasmanian Aquaculture and Fisheries Institute (TAFI), community volunteers and Break O’Day Council staff. Another indicator, macroinvertebrate fauna, was sampled by TAFI in winter and summer, and data were obtained on pathogen levels from the Tasmanian Shellfish Quality Assurance Program.