Data on physical conditions in Ontario’s lakes and streams: * For lakes this includes measurements such as temperature, dissolved oxygen levels and water transparency, ice dates, as well as sampling location details. * For streams this includes measurements such as stream flow discharge from monitoring stations in south-central Ontario. Meteorological conditions for climate stations close to monitored lakes in south-central Ontario, includes measurements such as air temperature, humidity, precipitation and wind speed. This data set includes information on sampling locations and physical conditions in lakes and streams across Ontario, as well as meteorological and lake ice-cover conditions from monitoring stations in south-central Ontario. Data were collected since 1976, as part of routine monitoring of water quality of inland waters and for scientific and research purposes. Keywords: water quality, meteorology, hydrology, wind, dissolved oxygen, environmental monitoring