Dataset: Environmental observations, physico-chemical data, chlorophyll, total and dissolved nutrients, plankton taxonomic classification, and cell abundance from surveys of Lake Erie from November 2024 to March 2025

The vessel came to a stop when the predetermined sampling station was reached, at a time decided on by the ship's command. The location and time of sampling were recorded, as well as the environmental conditions. The trained crew members of the vessel then used a YSI water quality sonde to collect data that were recorded. A Secchi disc with measurement indicators every 10 centimeters was then deployed, and recordings were taken on both the upcast and downcast. A Van Dorn water sampler was then used to collect water at a depth of 1 meter. Water samples were then transferred to 1-liter (L) polyethylene storage bottles or 2 L plastic storage bottles, and stored in a dark place at 4 degrees Celsius until picked up by personnel on the same day. The samples were then transported in dark coolers containing ice packs to Bowling Green State University (BGSU) or the University of Windsor (GLIER). Samples were also collected from Mitchell's Bay (a land-based sampling location) using the same methods and observational conventions.

Sub-samples for chlorophyll a were taken in the laboratory using 0.45 micrometer (um) nylon and 20 um polycarbonate membranes and a vacuum filtration system. The filter was placed in a screw cap polyethylene centrifuge tube and stored in a dark freezer until extraction. The samples were extracted using 90% acetone and kept at -20 degrees Celsius for 24 hours, and chlorophyll was measured using a TD-700 fluorometer (Welschmeyer, 1994).

Total and dissolved nutrient samples were held in acid-washed 250 milliliter (mL) polyethylene bottles and stored in a dark freezer at -20 degrees Celsius until they were ready to be analyzed. Dissolved nutrient sub-samples were taken by filtering the agitated sampled water through 0.22 um filters. The frozen samples were then shipped on ice to the National Center for Water Quality Research at Heidelberg University (Tiffin, OH). Microscopy was performed on raw water samples that were preserved with 5% Lugol's iodine solution. These samples were stored at room temperature in the dark until shipped and analyzed by Aquatic Taxonomy Specialists (Malinta, OH).