Medina Lake, an artificial reservoir in the Texas Hill Country, serves as a vital water source for agriculture, municipalities, industry, and recreation. Formed by the Medina Dam, approximately 40 miles northwest of San Antonio, the lake’s water levels have shown a notable and persistent decline in recent years. This reduction presents challenges for all sectors relying on its resources.
Historical Patterns of Water Levels
Since its completion in 1913, Medina Lake has experienced significant water level fluctuations due to the region’s variable climate. Historically, heavy rainfall led to near overflows, while droughts caused diminishment. For example, after a severe drought from 2010 to 2014, the lake recovered to 100% capacity by June 2016 and again in July 2019, demonstrating its capacity for replenishment. However, recent declines have been prolonged and severe, with the lake reaching as low as 2.4% capacity in June 2024 and 2.1% in April 2025, indicating a more persistent challenge than past cycles.
Climatic Contributions
Natural weather patterns significantly influence Medina Lake’s water levels. Prolonged droughts, with below-average rainfall, reduce water inflow from the Medina River and its tributaries. This precipitation deficit contributes to the lake’s decline. The Texas Hill Country’s arid to semi-arid climate intensifies these effects, making the region susceptible to extended dry spells.
Elevated temperatures and heat waves increase water loss through evaporation from the lake’s surface. As the sun warms the water, it turns into vapor and rises into the atmosphere, continuously reducing the lake’s volume. This process significantly depletes the lake, especially during hot, dry conditions. Without adequate rainfall to offset these losses, levels continue to drop.
Human Demands and Management
Human activities and water management practices also contribute to Medina Lake’s declining levels. A significant portion of the lake’s water is diverted for agricultural irrigation, managed by the Bexar-Medina-Atascosa Counties Water Control and Improvement District No. 1 (BMA). An extensive canal system, designed to operate by gravity, delivers water to approximately 33,000 acres of farmland. These diversions, particularly during dry periods of high agricultural demand, reduce the water remaining in the lake.
Beyond agriculture, Medina Lake water supplies municipal needs for surrounding communities. This constant demand for drinking water and domestic uses further reduces the lake’s volume. The Medina Lake Dam also releases water for downstream users or to maintain minimum flows in the Medina River. These releases, while serving specific purposes, affect the reservoir’s overall volume.
Geological Factors
The Medina Lake region’s geology contributes to its natural water loss. The area features karst topography, formed by the dissolution of soluble rocks like limestone, which is abundant in the Texas Hill Country. This creates a network of underground fissures, caves, and sinkholes beneath and around the lakebed.
Water from Medina Lake seeps into these highly permeable underground formations, causing continuous water loss into the groundwater system. This seepage recharges the Edwards Aquifer, a significant regional water source. While natural, this process contributes to the overall water deficit, especially when rainfall and river inflows are low. The U.S. Geological Survey estimates approximately 3,000 acre-feet of water seeps into the Edwards Aquifer from the lake monthly.