Recreational and Commercial fisheries and the quality of aquatic habitats in which the fish live are an important part of the livelihoods and economy of the Oregon Coast. The composition of important juvenile fish assemblages in estuaries can bring a unique view into the needs of different species on a seasonal scale, and can reveal the rearing needs of individual species based on their separate life histories. Environmental conditions along with documented seasonal patterns provide information to identify seasonal and temporal patterns of fish assemblages. Without baseline information, it is difficult to predict future use of estuarine habitat and aquatic chemistry changes as environmental and land use conditions change. The focus of this research is to evaluate seasonal, temporal, and tidal patterns of these fish assemblages at tide-gate locations in estuaries, as well as season and geographical patterns of stream aquatic chemistry. To examine these relationships samples of fish assemblages were collected using a beach seine net, at three tide-gated stream mouths entering northeastern portion of the Coos Bay Estuary from 2014-2018. In the four year period 16 species and 25,000 fish were captured. At high tide 8,000 fish were observed compared to 17,000 at low tide. Two samples were taken per tide at each location per season. The three sites represent different upstream watershed characteristics as well as separate estuarine habitat conditions which may reflect differences in fish assemblage compositions in those locations. Aquatic chemistry analysis included selecting 10 sites from the Inland side of Mary’s Peak to the coast. Samples were collected on a monthly for one year in 2016/2017 beginning in October. Major cations and anions were analyzed in the laboratory and examined for spatial, temporal and geographical patterns. Coastal sites were more correlated with sodium and chloride, where inland sites were more correlated with calcium and magnesium. Nitrate exhibited a seasonal pattern, flushing from the season upon the first fall rains and being recorded in the highest concentrations at this time. Calcium and magnesium exhibited opposite patterns of being measured in the highest concentrations during the low flow summer months. This research has filled a lack of understanding in aquatic ecology for both the fields of fisheries and aquatic chemistry. Collecting this baseline data will support future research in fisheries management and coastal stream water quality.