Sydney Inlet is the most northernmost body of Clayoquot Sound. The inlet is a glacially carved fjord estuary fed by the Sydney River. It is roughly 23.5 km long with a 25 m deep sill at the mouth, the bathymetry holds a deep cliff at 65 m deep that drops to an incredible 130 m, between stations 65 and 70 (roughly 15-19 km inland from the coast, near where Sydney intersects with Stewardson Inlet). The fjord has a relatively narrow, mile wide surface north of the meeting between Sydney and Shelter Inlet. Sydney Inlet is a uniquely quiet and highly preserved region, holding just one cabin used strictly for estuarine and ecological research.

Samples were collected for this study on September 12, 2015. On this date, temperature increased through the morning from a minimum at 06:00 to a maximum at 14:00. Pressure increased until midday, then decreased to below the morning's pressure. The morning had low wind speeds with large directional shifts. As air pressure dropped, wind speed increased nearly constantly from 09:00 until 18:00. Wind direction remained relatively constant from 13:00 through the rest of the day.

Deeper waters are colder and more stratified than at the surface, due to the lack of mixing, though between stations 63-64 there appears to be some mixing at depth. Sydney Inlet water is warmer than 2013 trends. In the basin, salinity is very high at 32 PSU. Salinity increases with depth, though it is fairly uniform throughout past approximately 20 m. At depth, inlet salinity is greater than 2013 levels, however in 2015 there is a surface freshwater layer extending from head to mouth.

Density stratification trends follow temperature, with some mixing between sites 63-64. Similar to the trend of salinity, a high density surface layer exists from head to mouth that did not appear in 2013. Maximum density in the deep basin was similar to 2013. Between surface and the deep basin, 2015 waters were less dense than pre-blob. Greater oxygen exists nearer the surface and decreases with depth to a very low oxygen condition in the deepest part of the fjord, due to the low mixing and low productivity of phytoplankton. Some mixing is suggested at the sill between sites 63-64, in the same area indicated by temperature and density. Even at surface, oxygen was lower in 2015 than in 2013, possibly due to the low phytoplankton productivity seen in the following charts.

Significantly, no fluorescence is shown in Sydney Inlet in 2015, even at surface. Transmissivity is also extremely low in this year, with only some slight percentage at the surface. This indicates very low or absent activity of plankton in the area, with some plankton existing near the surface. Transmissivity near the sil may be from sediment. Both charts indicate much less activity than in 2013.