This data set contains long-term limnology data from Castle Lake (located 5440 ft above sea level in Northern California) on primary productivity, zooplankton and phytoplankton measurements, dissolved oxygen, nutrient chemistry, lake morphology, and fish measurements. Short-term research projects on benthic invertebrates composition and a bathymetric map can also be found within the data package. Ecological, watershed and climatological measurements taken characterize the limnology of Castle Lake, a pristine glacial cirque that is the largest (by volume) of the 25 alpine and sub-alpine lake within the larger Upper Sacramento River Watershed. Sampling Frequency: Varies depending on survey conducted. During summer months- multiple times during each month. Less frequent during winter months. This data collection part of an ongoing project funded by the US National Science Foundation, private donors, US AID, and the University of Nevada's Global Water Center.