Zooplankton data from the two Sudbury lakes (Middle and Hannah). Pelagic crustacean zooplankton were sampled in each lake on a monthly basis from 1973 to 1992. These data are in tab-delimited ASCII format, without column headings, in MEHHZOO.TXT. N.B. Samples with missing biomass estimates in the years 1973 to 1984 were counted using a different protocool than the rest of the samples.