This dataset includes zooplankton and water quality data from 37 lakes sampled in the Northwest Territories, Canada, from the Dempster and Inuvik-Tuktoyaktuk Highways during July and August of 2017 and 2018. It was collected as part of a project to determine how physicochemical variables affect zooplankton and fish communities in small Arctic lakes.

Our study includes 37 lakes located along the Dempster and Inuvik-Tuktoyaktuk Highways in the Northwest Territories. Lakes along the Dempster Highway were sampled between August 17^th and September 1^st, 2017 while lakes along the Inuvik-Tuktoyaktuk Highway were sampled between August 6^st and August 27^th, 2018.

We collected data on surface area and maximum depth for each lake by constructing bathymetric maps using a Humminbird Helix 5 chartplotter (Johnson Outdoors Marine Electronics, Inc), in combination with Reefmaster bathymetry software (Reefmaster Ltd.). We also collected water quality data including Secchi depth (water clarity), turbidity, conductivity, dissolved oxygen (DO), pH, total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), calcium, chlorophyll-a, and water temperature (Table 1). To obtain water clarity measurements, we lowered a Secchi disk over the shady side of the boat at the deepest point on the lake. At the same location, we measured turbidity, conductivity, DO, pH, and temperature, using a Manta+ multiparameter probe (Eureka Water Probes) at a depth of 1 m. We also collected water for the measurement of TOC and calcium levels at the same site using a 3 m polyethylene integrated tube sampler. We used a Perkin Elmer Optima 8000 Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) instrument to measure calcium concentrations, and a Shimadzu TOC-LCPH Carbon and Nitrogen analyzer (Shimadzu Corp.) to measure TN and TOC. We collected surface water samples from the shoreline of each lake for chlorophyll-a and TP measurements. To measure TP, we digested samples in an autoclave with ammonium persulfate and sulfuric acid following EPA method 365.1. We then used SEAL method G-103-93 to measure TP colorimetrically using the SEAL Continuous Segmented Flow Analyzer (SEAL Analytical, Inc.). To measure chlorophyll-a levels we filtered 250 mL water samples through Fisherbrand G4 glass fiber filters, extracted chlorophyll­-a from the filters using methanol, and analyzed the quantity of chlorophyll using a Turner TD700 fluorometer.

We collected zooplankton samples from each lake at the point of maximum depth and preserved them on site using 95% ethanol. For lakes greater than 3 m in depth, we collected a single vertical haul using a 35-cm diameter, 50 μm mesh size zooplankton net. For shallow lakes less than 3 m in depth, where a vertical tow was not possible, we collected zooplankton by towing the net behind the boat for approximately 60 seconds. In both cases, we used a mechanical flowmeter attached to the mouth of the net to determine the volume of water that passed through the net. In the laboratory, we identified crustacean zooplankton to the species level according to Haney et al. (2013) using a magnification of 40x to 400x depending on the size of the species. We identified rotifers to the genus level using the same classification key by examining samples in a Sedgewick Rafter counting slide at 40-400x magnification.

Haney, J.F., Aliberti, M.A., Allan, E., Allard, S., Bauer, D.J., Beagen, W., Bradt, S.R., Carlson, B., Carlson, S.C., Doan, U.M., Dufresne, J., Godkin, W.T., Greene, S., Kaplan, A., Maroni, E., Melillo, S., Murby, A.L., Smith, J.L., Ortman, B., Quist, J.E., Reed, S., Rowin, T., Schmuck, M., Stemberger, R.S., and Travers, B. 2013. An image-based key to the zooplankton of North America, version 5.0. Available from http://cfb.unh.edu/cfbkey/html/.