Grand Teton National Park Trophic State Evolution at 33 Locations in 29 Lakes over Three Decades: Field Data and Analysis

We present a 30-year analysis of water quality trends in Grand Teton National Park, based on 715 sampling events we collected at 33 locations across 29 lakes from 1995 to 2025. Our dataset includes Secchi depth, chlorophyll-a, and total phosphorus, collected seasonally from both in-lake and inlet sites. We classified lake trophic states using the Carlson Trophic State Index (CTSI) and the Vollenweider (VW) and Larsen–Mercier (LM) models. Most lakes remain mesotrophic (CTSI 38–54), with larger lakes such as Jackson and Phelps showing lower total phosphorus, while smaller lakes like Christian Pond and Cygnet Pond exhibit higher chlorophyll-a. High-elevation lakes generally have reduced nutrient concentrations. Seasonal effects are pronounced, with late summer and fall samples—especially at Swan Lake and Two Ocean Lake—showing increased chlorophyll-a. Trend analysis using the Mann–Kendall test identified statistically significant decreases in chlorophyll-a for six lakes and in total phosphorus for fifteen lakes; no lakes showed significant increases in any parameter. Four lakes—Christian Pond, Swan Lake, Two Ocean Lake, and Oxbow Bend—demonstrated consistent improvements across all measured indicators. The magnitude of these declines was modest, suggesting gradual oligotrophication rather than widespread eutrophication. Our comparison of trophic state models highlights that VW and LM often assign higher trophic classifications than CTSI. This study provides a robust baseline for understanding the resilience of high-elevation lakes in Grand Teton National Park. Our unique dataset, collected from remote and often barely accessible sites, is publicly available to support future research and management. Continued monitoring is essential to detect potential impacts of climate change and human activity, ensuring the preservation of these sensitive aquatic ecosystems.