This is the 9th annual report of the Oklahoma Water Resources Research Institute. The most pressing water problems of the State continue to be in water resources planning. Oklahoma is mining water from the Ogallala Aquifer at a rate far in excess of natural recharge. This and other groundwater problems (surface subsidence and groundwater pollution) are currently being discussed at a series of regional conferences sponsored by the OWRR and the regional Institute directors. For the past several years, the Institute and affiliated university researchers have been studying the effect of eutrophication and summer stratification on the water quality and ecosystems of lakes and reservoirs. (Modified author abstract)