Yearling coho salmon (Oncorhynchus kisutch) were exposed for 12 wk to either 0.3, 1.1, or 3.6% chlorinated municipal sewage treatment plant effluent with seawater diluent (average salinity 28‰)under continuous flow conditions. The maximum safe concentration of effluent lies between 0.3 and 1.1% (average total residual chlorine (TRCl2) content 0.003 and 0.009 mg/liter, respectively). Effluent concentrations of 0.3% produced no discernible effects on the fish. Concentrations of 1.1 and 3.6% (average content of TRCl2 0.030 mg/liter) resulted in reductions of hemoglobin and hematocrit to levels indicative of anemia. Observations of the erythrocytes revealed lysed and degenerating cells, increased numbers of circulating immature cells, and abnormal cells. These hematological effects are attributed to the oxidative nature of TRCl2.

The seasonal periodicity of periphyton growth in the Duwamish estuary (Washington) is compared with that of phytoplankton and lends support to a previous conclusion that hydrographic conditions determine the timing of phytoplankton blooms despite high concentrations of dissolved nitrogen and phosphorus. Accumulation of periphyton on substrates increased in June and July to around 10 µg Chl a cm−2 week−1 and is related to incident light; conversely, phytoplankton blooms were delayed until August and September when hydrographic conditions were optimum for biomass accumulations of from 30–70 µg Chl a/liter. Maximum growth of periphytic and planktonic algae occurred at the same location in the estuary. This similarity in spatial distribution is not directly related to hydrographic conditions since the periphyton algae are sessile and more resistant to washout. The water in this section of the estuary presumably contained a more adequate supply of one or more limiting nutrients than water from adjacent locations.