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Spatial and Seasonal Water-Quality Patterns and Temporal Water-Quality Trends in Lake Conroe on the West Fork San Jacinto River Near Conroe, Texas, 1974–2021

Scientific Investigations Report 2025-5015
Prepared in cooperation with the San Jacinto River Authority
By:
https://doi.org/10.3133/sir20255015

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Abstract

The impoundment of Lake Conroe in 1973 created an important water resource for greater Houston, Texas. The U.S. Geological Survey, in cooperation with the San Jacinto River Authority, analyzed water-quality data collected from 1974 to 2021 at upreservoir, mid-reservoir, and downreservoir sites in Lake Conroe. Water-column and seasonal variability of selected water-quality constituents (physiochemical properties, major ions, nutrients, and trace metals) were assessed, as well as thermal stratification. Water-quality trends were evaluated for 1974–2021 and 1993–2021.

Near-surface water (1–3 feet below the water surface) was warmer and contained higher dissolved-oxygen concentrations compared to near-bottom water (2–3 feet above the reservoir bottom). Dissolved-oxygen concentrations were lowest in summer and highest in winter. Specific conductance was higher near the bottom and varied seasonally, being lowest in winter and highest in summer. Values of pH were generally higher at the surface, with some variability between sites and seasons. Water transparency was higher downreservoir and seasonally lowest in summer.

Major-ion concentrations varied minimally within the water column and seasonally, except for sulfate, which was higher in winter and lower in summer. Most nutrient and trace metal concentrations were highest near the bottom during summer, notably at deeper sites. Thermal stratification in Lake Conroe begins in spring and peaks in summer and was limited to the deeper parts of the reservoir. The seasonal variability observed in dissolved constituent concentrations was driven by thermal stratification. Trend analyses for 1974–2021 indicated positive trends in water temperature, dissolved oxygen, pH, potassium, sodium, and silica. Negative trends were detected for calcium and magnesium near the reservoir bottom. During 1993–2021, positive trends were detected for near-surface dissolved-oxygen concentration, specific conductance, pH, all major ions excluding sulfate, and near-surface ammonia plus organic nitrogen concentration. Negative trends were determined for ammonia, iron, and manganese concentrations. Water transparency generally decreased over time.

Suggested Citation

Adams, A.C., 2025, Spatial and seasonal water-quality patterns and temporal water-quality trends in Lake Conroe on the West Fork San Jacinto River near Conroe, Texas, 1974–2021: U.S. Geological Survey Scientific Investigations Report 2025–5015, 114 p., https://doi.org/10.3133/sir20255015.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Methods
  • Spatial and Seasonal Water-Quality Patterns in Lake Conroe
  • Water-Quality Trends in Lake Conroe
  • Study Limitations and Considerations for Future Work
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Spatial and seasonal water-quality patterns and temporal water-quality trends in Lake Conroe on the West Fork San Jacinto River near Conroe, Texas, 1974–2021
Series title Scientific Investigations Report
Series number 2025-5015
DOI 10.3133/sir20255015
Publication Date April 09, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Oklahoma-Texas Water Science Center
Description Report: x, 114 p.; Dataset
Country United States
State Texas
City Conroe
Other Geospatial San Jacinto River
Online Only (Y/N) Y
Additional publication details