The chemical and physical properties and the range of concentrations of most constituents in water in the Pascagoula and Escatawpa Rivers during the period May 17-19, 1977, varied rapidly between high and low tides, primarily as the result of interactions of freshwater inflow with highly mineralized Gulf waters. The water at a downstream site of the 11-mile study reach on the Pascagoula River was saline. On May 19, 1977, the dissolved-solids concentration at that site was 14,500 milligrams per liter. At the same time, the water at the mouth of Escatawpa River had a dissolved-solids concentration of 4,600 milligrams per liter. The specific conductance of the water at the downstream sites of both rivers increased with depth and progressively decreased upstream to sites where freshwater inflow was predominant. The specific conductance decreased upstream from a maximum of 40,000 micromhos per centimeter at 25°Celsius at site P1 to 60 micromhos at site P12 on Pascagoula River and from 30,000 micromhos at site E1 to 45 micromhos at site E9 on Escatawpa River.

There was evidence of oxygen deficiency (less than 3.0 milligrams per liter) at many sites in deep pools where there is little circulation and mixing of the more dense saltwater. Dissolved-oxygen concentrations ranged from 2.1 to 8.2 milligrams per liter.

Biochemical oxygen demand ranged from 0.1 to 3.5 milligrams per liter and was generally less than 2.0 milligrams per liter at most sites.

A large part of the total organic carbon in the lower Pascagoula River was carried into the study area by freshwater inflow. Very little organic carbon was being discharged by the Escatawpa River into the Pascagoula River.

Total nitrogen moved out of Pascagoula and Escatawpa Rivers at an extremely slow rate and in concentrations of less than 0.1 milligram per liter.

The water temperature near the surface at downstream sites on Escatawpa River at low tide was elevated as much as 2.5°C (4.5°F), suggesting thermal loading.

The fecal coliform and fecal streptococcal bacteria in Pascagoula and Escatawpa Rivers were in concentrations indicative of manmade pollution. The ratio of the concentrations in which these bacteria were present suggests that both rivers receive human enteric wastes.