Entrainment of fish larvae and eggs was monitored at the J. H. Campbell Plant, eastern Lake Michigan, from 1977 to 1979. A procedure for calculating error bounds for estimated number of fish larvae (or eggs) entrained by the plant for each year of operation, assuming independence among observations, was outlined. A new method for calculating these bounds was devised by adjusting the variance for its non-independent component, using time series analysis. Serial correlation in the data was accounted for by modeling the sequence of entrainment data for a year as a time series. For many taxa of fish larvae the entrainment observations were determined to be independent and no adjustment was necessary. The width of the adjusted error-bound intervals ranged from 4.8 to 87.9% greater than unadjusted ones for those taxa for which adjustment was required, thus assuming independence among observations could result in serious underestimation of the error-bound interval.Key words: error bounds, variance, entrainment, Lake Michigan, serial correlation, time series analysis