Copper-based pesticides are commonly used in freshwater systems to manage algae and invasive species such as zebra mussels (Dreissena polymorpha), but concerns persist regarding their effects on non-target organisms. This dissertation integrates findings from a systematic literature review, an analysis of lake-scale treatment projects, and field-based experimental research to evaluate the ecological effects and management implications of copper use in lakes.

Chapter 1 presents a systematic review of 580 peer-reviewed articles, synthesizing results from 6,271 experiments involving 418 species. Most studies assessed short-term toxicity, often using copper sulfate, and 89.4% reported LC₅₀ values below 1 mg Cu/L—indicating that harmful effects can occur below U.S. EPA label rates. However, inconsistent reporting of key water chemistry parameters (e.g., pH, dissolved organic carbon) limited cross-study comparisons and assessments of copper bioavailability.

Chapter 2 reviews 33 zebra mussel control projects across 23 North American lakes. Three key factors emerged for effective and safe management: (1) using pre- and post-treatment surveys designed to capture all life stages; (2) defining treatment areas that fully encompass target populations; and (3) collecting water chemistry and non-target effect data to inform adaptive management.

Chapter 3 evaluates a whole-lake copper treatment (60 µg Cu/L for 10 days) in Lake Minnetonka, Minnesota. We assessed impacts on native mussels, fish, zooplankton, and benthic invertebrates. Zooplankton communities declined initially but recovered within a year; benthic invertebrates showed no significant long-term changes. Copper bioaccumulation was highest in bivalves, with some variation among fish species.

Chapter 4 supports site-specific decision-making by testing the Biotic Ligand Model (BLM) and multiple linear regression (MLR) approaches to predict lethal concentrations based on water chemistry. In a mobile-laboratory experiment, observed LC₅₀ values for Daphnia magna aligned closely with BLM predictions, underscoring the utility of modeling tools for guiding copper application.

Together, these findings highlight the complexity of copper toxicity in freshwater systems and emphasize the need for better water chemistry reporting, predictive modeling, and thoughtful management design to balance invasive species control with ecosystem protection.