Explore Your Watershed

The National Geographic Society describes a watershed as: 

...an area of land that drains or “sheds” water into a specific waterbody. Every body of water has a watershed. Watersheds drain rainfall and snowmelt into streams and rivers. These smaller bodies of water flow into larger ones, including lakes, bays, and oceans. Gravity helps to guide the path that water takes across the landscape.

Not all rain or snow that falls on a watershed flows out in this way. Some seeps into the ground. It goes into underground reservoirs called aquifers. Other precipitation ends up on hard surfaces such as roads and parking lots, from which it may enter storm drains that feed into streams.

Watersheds can vary in size. A watershed for a tiny mountain creek might be as small as a few square meters. Some watersheds are enormous and usually encompass many smaller ones. The Mississippi River watershed is the biggest watershed in the United States, draining more than three million square kilometers (one million square miles) of land. The Mississippi River watershed stretches from the Appalachian Mountains in the east to the Rocky Mountains in the west. Thirty-one U.S. states and two Canadian provinces fall within the Mississippi River watershed.


Probably few people give special notice or thought to their watershed. But let's see what happens if we try to become part of our watershed community by learning about it through information and experience. What we describe below is based on our home watershed, the San Marcos River, but the process will work for virtually all watersheds.

The San Marcos is part of the larger Guadalupe River watershed that flows into San Antonio Bay, which is part of the large chain of bays behind Texas' barrier islands on the Gulf of Mexico.


The learning process outlined below is place-based and inquiry-based. We offer a few questions to get you started, the further and farther you go, the more you will find to be interested in. We're not recommending that you drive unnecessary miles, but if you really need to get away, explore the Guadalupe River watershed rather than going farther away. Maybe you'll find a farmer's market, and we know you will find great BBQ and seafood!

Click on the image below to go to the Guadalupe-Blanco River Authority's tremendous interactive website to help you learn all about the Guadalupe River watershed. 

For more detail about the Guadalupe River system, click on the image below:

The San Marcos: A River's Story is a useful book about that river and its watershed. It is available in the San Marcos Public Library and in the Texas State University library. 

Go to the online book Texas Aquatic Science, which provides a wonderful background for understanding all of the state's waters. Also, look at the Handbook of Texas History's pages about the Guadalupe, Blanco, Comal, and San Marcos rivers.


On Google Earth, go to Canyon Lake, which is a very large reservoir formed by a dam built on the Guadalupe River. "Fly" up and down the river, just to see what you can see.


Here are some questions and suggestions to prompt your study of the Guadalupe River watershed. These are not assigned questions, only suggestions as a starting place.