Historical water temperature (and Secchi depth) profile and multi-agency monitoring records for Lakes Ontario and Huron

This dataset contains historical water temperature and water clarity (Secchi depth) records for Lakes Huron, Erie, Ontario, and St. Clair, compiled by Norine E. Dobiesz. The Ontario and Huron profile/station data were originally compiled by Dobiesz and Lester (2009) and are included here with prior permission; additional climate, light, and Erie/St. Clair records were compiled as part of related project reports (Dobiesz 2005, 2006). Data were assembled from multiple agencies (DFO, Environment Canada, GLERL, GLINPO, and EPA/Storet) and include secchi depth, percent light transmission, extinction coefficients, turbidity, water temperature profiles, dissolved oxygen, air temperature, and water levels, collected via mid-lake buoys, water treatment intake stations, and field sampling programs. Each lake was divided into ecologically distinct regions (e.g., Lake Erie's western, central, and eastern basins; Lake Huron's main basin sub-regions plus Saginaw Bay, Georgian Bay, and the North Channel; Lake Ontario's western, eastern, and outlet basins plus the Bay of Quinte) and further classified by nearshore (≤10 m) versus offshore (>10 m) station depth. Observations were organized into three time periods reflecting major environmental shifts in the Great Lakes: pre-phosphorus control (1968–1981), post-phosphorus control/pre-zebra mussel invasion (1982–1988 or 1982–1992, lake-dependent), and post-zebra mussel establishment (1989/1993–2002). The database structure follows a relational format with station information, temperature/oxygen depth profiles, and light/turbidity profiles as separate linked tables (see accompanying Data Dictionary). Seasonal patterns were also characterized by grouping observation months into mixing periods (May, Oct) versus stratified periods (Jul, Aug), given that these two windows captured the clearest seasonal contrast with the least data-gap sensitivity. This dataset supported analysis of long-term and seasonal trends in water clarity and temperature across the Great Lakes, including their relationship to phosphorus abatement, dreissenid mussel invasion, and major weather/climate events (e.g., El Niño/La Niña cycles, the 1991 Mt. Pinatubo eruption), with particular relevance to walleye thermal-optical habitat. Erie_Profile.xlsx / Huron_Profile.xlsx / Ontario_Profile.csv: depth-resolved water temperature and dissolved oxygen profiles by station and date (Erie: 1967–2002; Huron: 1970–2002; Ontario: 1960–2002). St. Clair profile data (StClair_Profile.xlsx) is currently empty (0 records). Erie_Station.xlsx / Huron_Station.xlsx / Ontario_Station.csv / StClair_Station.xlsx: multi-agency (DFO, NWRI, Environment Canada, US EPA, GLNPO, water intake stations, buoys, OMNR, GLERL) surface temperature and Secchi depth (water clarity) records (Erie: 1960–2004; Huron: 1923–2003; Ontario: 1960–2003; St. Clair: 1930–2003). Note: Huron_Station.xlsx contains one record with an anomalous date (1900), likely a data entry artifact. Erie_Climate.xlsx / Huron_Climate.xlsx / Ontario_Climate.xlsx / StClair_Climate.xlsx: monthly air temperature summaries (mean, min/max with dates) by station (Erie: 1968–2002; Huron: 1968–2002; Ontario: 1968–2002; St. Clair: 1968–2003). Erie_Light.xlsx / Huron_Light.xlsx / Ontario_Light.xlsx: depth-resolved percent light transmission, extinction coefficient, turbidity, and KPAR by station and date (Erie: 1973–2003; Huron: 1961–2003; Ontario: 1972–2003). St. Clair light/turbidity data (StClair_Light.xlsx) is currently empty (0 records). All files include a Period field (1 = pre-phosphorus control, 2 = post-phosphorus control, 3 = post-zebra mussel invasion).