SAN MARCOS—San Marcos’ population growth can have a significant impact on the San Marcos River, as the spread of invasive species is typically caused by human interaction.
Over the past decade, nearly 20,000 people have moved to San Marcos. As more people continue to move into the area, it can have a significant impact on the San Marcos River. Humans can have a significant impact on the river’s ecosystem, whether that be a positive or negative effect. The greatest cause for concern rises with the spread of invasive species and pollution.
Texas State student Dylan Sonntag is one of many who moved to San Marcos within the past few years. He began attending Texas State in fall 2018, he said the San Marcos River was one of the biggest reasons why he chose to attend Texas State.
“Yeah, I feel like it’s like the heart of San Marcos, like I think that’s the best thing on campus,” Sonntag said. “I feel like that’s a lot of reason that people come to Texas State is to go check out the river and chill there.”
During the summer, Sonntag said he will spend between one to four hours every day with his friends at the San Marcos River. He said the activities range from swimming, tubing and picnicking. Sonntag said that sometimes he’ll even find people scuba diving in the river.
The San Marcos River runs directly through the city of San Marcos. The San Marcos River serves as a tourist hotspot for the city. (Photo credit: Dean Trevino) 
Texas State University, located in San Marcos, TX. In fall 2021, Texas State had nearly 38,000 students attending. (Photo credit: Dean Trevino) 
Many San Marcos residents and visitors enjoy the river by kayaking. The group began their adventure with Sewell Park Outdoor Center. (Photo credit: Dean Trevino) 
Tubing is another of the many ways that San Marcos residents and visitors can enjoy the San Marcos River. The group began their tubing adventure with Don’s Fish Camp. (Photo credit: Dean Trevino) 
San Marcos residents and visitors are required to have a fishing license before they fish in the river. Fishing is another way to combat the spread of invasive species like Plecos and Blue Tilapia. (Photo credit: Dean Trevino)
The San Marcos River is currently experiencing issues with invasive species, which include suckermouth catfish, cryptocoryne and blue tilapia. The vast majority of invasive species are typically introduced through human interaction. Invasive species can spread to other bodies of water through contaminated boat ballasts, contaminated fishing equipment and dumping aquariums.
Texas State University Biology Professor Timothy Bonner said the suckermouth catfish is a very popular fish sold in stores. He said people will buy suckermouth catfishes along with various plants for their aquariums. He said the suckermouth catfish can grow to a couple feet and become too large for aquariums, some people will illegally release the fish into the river. The suckermouth catfish serves as a bottom feeder, and will eat eggs and fish in the river bank.
“We’ve really targeted like Texas State students because they’re here for a short time they may develop an aquarium,” Bonner said. “I think that’s a population that we’re making sure that whenever they move that they’re not taking their aquarium and dumping it in.”
Bonner said that parasites have also been introduced through illegally releasing species into the river. This adds an additional layer of issues with protecting the San Marcos River.
“It’s just not the species that you’re putting in the system, like the snail or the fish. It’s also any disease that they may carry,” Bonner said.
Randy Gibson, supervisory biologist at the San Marcos Aquatic Resources Center, said that there’s highways that cross the river. Thus raising any potential concerns for chemical spills that can pollute the river.
“If there’s spill pollution, that can cause some major issues, and that’s another thing that we have to worry about is pollution of the groundwater,” Gibson said. “Citizens of San Marcos need to make sure so that that their septic systems are functional and not leaking, and of course, not dumping any kinds of chemicals in their yard or in the river.”
Gibson said if San Marcos citizens are interested in preserving the river, that there are volunteer groups at Texas State and all around San Marcos. Gibson said to ensure the river is protected, for San Marcos citizens to follow the rules and not to destroy the habitat by pulling out the vegetation.
“Follow the rules that are there and try not to when you’re in the river, you’re not ripping things up or, you know, destroying habitat, then everything will be fine,” Gibson said. “And also, if they see other people and other things that going on, report it to Parks and Wildlife.”
Yovani Valdes (left) and Intern Kevin Rubio (right) are maintaining various plants that can be found within the San Marcos River. The raceway is meant to mimic the San Marcos River. (Photo credit: Dean Trevino) 
The San Marcos Aquatic Center has a display of plants including Texas Wild Rice. Texas Wild Rice is an endangered species of plant that can only be found in the San Marcos River. (Photo credit: Dean Trevino) 
The San Marcos Aquatic Resources Center contains the EAA refugia, where they hold threatened and endangered species. They hold the various species for research and in the case of a catastrophic extinction event, so the species can be reintroduced into the wild after the habitat is restored. (Photo credit: Dean Trevino)
The San Marcos city website contains more information on how San Marcos citizens can volunteer to help protect the river. At the Meadows Center, there’s a group called the Habitat Field Crew, and they’re working to control non-native vegetation and grow Texas wild rice. The San Marcos River Foundation also accepts the help from volunteers for hot spot clean-ups.
A mural of San Marcos River mascot Sally Salamander promoting visitors to pick up their litter. The mural is located outside of San Marcos Lions Club Tube Rental. (Photo credit: Dean Trevino) 
The San Marcos River is currently suffering from low water levels, and as the water levels decrease, the Texas Wild Rice is revealed. The Texas Wild Rice is dependent on stable water levels and flow in order to survive. (Photo credit: Dean Trevino)
