abstract: From 2001 to 2003, we carried out a limnological investigation of Cultus Lake, B.C. The
lake was warm monomictic and thermally stratified from May-November each year.
Epilimnetic temperatures exceeded 20 degree C from June or July until September. Average
euphotic zone depths were 15.8 m, 2.5x deeper than average ephilimnion depths. Total
phosphorus averaged 7.4 pg/L (8.9 pg/L at spring overturn) and average values of a
number of chemical variables were the highest ever recorded in B.C. sockeye lakes. The
seasonal average daily photosynthetic rate of 449 mg C m-2 d -1 was also the highest
ever recorded in these lakes. A range of chemical and biological variables indicated
that Cultus Lake is mesotrophic and much more productive than most sockeye nursery lakes
in B.C. The zooplankton community was abundant and dominated by Daphnia throughout the
year. Data from this and from an earlier study indicate that Cultus Lake has warmed
substantially in the last 75 yr and there are a number of indications that its
productivity has increased as well.
