Invasive Species

On a walk or boat ride along the San Antonio River Walk, you may have seen some bright pink blobs above the water line adhering to the concrete or other structures. These are apple snail (Pomacea sp.) egg cases, and each egg case can contain thousands of eggs.

Apple snails are native to South America, and they are a threat to the San Antonio River ecosystem. This snail species has no natural predators in our area and their populations are continuing to increase. Apple snails thrive in the San Antonio River’s warm waters and can reproduce continuously 8 to 9 months of the year. The snails are voracious eaters of aquatic plants, and in many river systems, this can be detrimental to other river species that rely on plant resources. In many waterways and wetlands, depleting the native aquatic plants population can also affect how well an ecosystem functions to maintain good water quality, thus causing further havoc.

You may be wondering how the apple snail came to live in the San Antonio River. These snails were most likely purchased at a pet store or were uninvited stowaways on plants that were purchased by aquarium hobbyists. Full grown, these snails can be the size of a softball! Once the snails got a little too big for the aquarium, people may have been unsure of what to do with them and in an uninformed attempt to be compassionate, released them in the nearest waterbody.

The apple snail population increase is difficult to mitigate as they have many surprising adaptations. The apple snails avoid the ill-effects of a deep freeze, like the one in San Antonio in Winter 2021, by burrowing deep into the river’s natural sediment bottom and banks. While these snails lay their eggs above the waterline for respiratory and development reasons, it just so happens that the eggs benefit from staying out of the mouths of predatory fish. This snail is difficult to see, too, with green-brown shells camouflaged against the similar color of the naturally turbid river water. The apple snail can also float, allowing it to be easily be carried around a waterbody and lay eggs in new locations.

How does the San Antonio River Authority work to mitigate the apple snail population?

The San Antonio River Authority (River Authority) is proactive when it comes to protecting our natural resources and staff has been hard at work to address invasive species as part of our commitment to safe, clean, and enjoyable creeks and rivers. 

River Authority Environmental Science staff and Watershed and Parks Operations staff work in tandem to survey the river and have apple snail egg cases and adults collected, permanently removing them from the San Antonio River. Workers visit the Museum Reach section of the River Walk every 10 days to remove every egg case and snail they can find. This 10-day window is an advantageous tactic to mitigation of population growth because the egg cases take approximately 10 to 14 days to mature and hatch. Therefore, as best as possible, the collection and removal of the egg cases stays ahead of the hatching cycle of the snail.

It is illegal to possess or transport apple snails. The River Authority has been granted by Texas Parks and Wildlife Department (TPWD) the ability to work with members of the public to collect both adults and egg cases, through a training process. People interested in helping to mitigate the apple snail population growth can join the River Authority’s River Warriors volunteer group. The skilled science and volunteer staff will equip volunteers with the methods to remove the snail from the San Antonio River. By attending this training, individuals can collect and promptly dispose of adult apple snails by way of Active Partner Status through the TPWD.

If you are interested in helping us manage this invasive species or participating in any of our other volunteer service projects or educational trainings, please sign up and join the River Warriors.

Being Helpful from Home

Please remember, never dump your aquarium into the river or any other freshwater or saltwater body. You can keep up with the San Antonio River Authority efforts regarding apple snails and other invasive organisms, by following the River Authority on social media channels and by following the River Authority Blog.

Invasive Zebra Mussels have been discovered in lakes and waterways in South Texas. The San Antonio River Authority has begun coordinating efforts to reduce the risk of this damaging mussel affecting the San Antonio River Watershed.

Zebra mussels are native to Russia and the Ukraine. They were first detected in the United States in the Great Lakes and Hudson River in the 1980s. Since then, they have steadily made their way across the United States by hitching rides on boats traveling between streams and lakes.

Zebra Mussels multiply rapidly, the few natural predators in Texas waterways have little effect on their spread. Infested streams and lakes have reported colonies of zebra mussels taking over habitats and nutrients from native fish and mussel colonies.

They can also interfere with recreation and wreak financial havoc on infrastructure. Recreational users may face encrusted boat hulls and mechanical systems and damage to fishing equipment. Municipal water supply intake pipes and pipelines can become fully blocked as they are colonized by zebra mussels.

The River Authority’s goal is to stop this spread from reaching the San Antonio River watershed. Texas Parks and Wildlife Department (TPWD) and The River Authority advise both motorized and non-motorized boat recreationalists to do the following:

1. Clean your watercraft, anchor, trailer, and gear. Remove any plants, animals or foreign objects.
2. Drain all water from your watercraft and completely empty your bait buckets to rid them of possible microscopic zebra mussels and larvae.
3. Dry everything for a week or more before entering another water body. If unable to dry it completely, wash it with high-pressure, hot (140° F), soapy water.

You can also help to stop the spread by reporting any new sightings to TPWD. Visit TPWD’s www.texasinvasives.org website to learn more.

Please remember, never dump your aquarium into the river or any other freshwater or saltwater body. You can also report any sighting of egg cases or adult snails by calling toll free at (866) 345-7272 or contact us through our website. Your help with reporting this invasive species will assist our Environmental Sciences Team to further study and remove the presence of this non-native species along our creeks and rivers. Finally, we will soon be training volunteers to help us track and remove apple snail egg cases. If you're interested in helping us manage this invasive species or participating in any of our other volunteer service projects or educational trainings, please sign up and join the River Warriors.