Flowing from artesian springs, the San Marcos River emerges out of the Edwards Aquifer, forming Spring Lake. It flows southward to join the Blanco River and then the Guadalupe River 75 miles downstream.
A popular recreational spot, visitors to the river enjoy tubing, kayaking, swimming, snorkeling and fishing in the crystal clear water. It is also a rare and delicate ecosystem with numerous threatened and endangered species including the Texas Blind Salamander, the Fountain Darter and Texas Wild Rice. These, along with the San Marcos Gambusia and San Marcos Salamander, require clear, clean, continuously flowing water with a stable temperature.
The Edwards Aquifer itself is a unique groundwater system and one of the most prolific artesian springs in the world. It serves the diverse agricultural, industrial, recreational, and residential needs of over two million users in central Texas, including San Antonio with a population nearing 1.5 million.
The increased demand for water, however, coupled with massive growth in San Marcos (the fastest growing city in the nation for three years in a row) has raised issues concerning the depletion of the aquifer and decreasing flows. Particularly during periods of drought, the effect this has on threatened or endangered species and local economies is serious.
Inadequate flows lead to eutrophic conditions and increased salinity in Texas bays, affecting fish and wildlife populations and coastal economies. Texans are now facing difficult decisions regarding who owns and controls water from aquifers and what types of regulations are needed to protect them to ensure a steady, clean flow of water recharging into an aquifer and ultimately, springs that flow into the San Marcos River or other Texas rivers.
Other, more localized concerns involve the impact of heavy recreational use, what constitutes responsible development in the flood plains and sensitive areas around aquifer recharge zones, non-source point pollution, sewage and septic tank discharges, storm water run-off, the spread of invasive species and bank erosion.
The San Marcos River is considered to be one of the most biologically diverse ecosystems known in the southwestern United States and great care must be taken to ensure it remains clean, clear and flowing.