Spatial and temporal variability in water temperatures in the littoral zone of a multibasin lake

Current models of the offshore thermal structure in lakes suggest that the thermal regime inshore should vary seasonally, and should vary systematical ly from upwind to downwind littoral sites. To test these hypotheses, we mea sured mean temperature and short-term (<2 days) temporal variability in wat er temperature at 23 shallow littoral sites in four basins of Lake Opeongo, Ontario, Canada. Water temperature in the littoral zone was most variable, both spatially and temporally, in the spring. Spring water temperature dif fered by as much as 7-15 degreesC among littoral sites in different basins (median difference among sites = 2-4 degreesC). Downwind sites were general ly warmer and had more constant temperature than upwind sites, but the magn itude of these differences varied among basins of different sizes and shape s. Simple calculations of growth rates and of fish hatching times suggest t hat the observed variability in water temperature would result in differenc es in the productivity of different portions of the littoral zone.