Fishing the Floodwaters: Exploring How San Antonio Controls Its Floods

Published: Aug 12, 2026

Author: Edmund Winston

San Antonio is a city that has learned, often the hard way, how dangerous too much water can be.

After a series of devastating floods, including major flooding in 1921, the city began developing an extensive system of dams, channels, flood-control structures and, eventually, an enormous underground tunnel designed to keep floodwaters from overwhelming downtown.

I recently set out to explore some of those flood-control areas around San Antonio. Of course, I brought a fishing rod along. If I was going to be standing next to the water anyway, I figured I might as well see whether anything was willing to bite.

The trip turned out to be as much about San Antonio history as it was about fishing.

Fishing in the Aftermath of the Floods

July 2025. The area had been dealing with an incredible amount of rain.

Major flooding had recently affected the San Antonio area and the Texas Hill Country, with catastrophic consequences farther upstream. Communities around Kerrville, Hunt and other Hill Country towns were hit especially hard, and the continuing rain was complicating recovery efforts.

For me, the flooding hit particularly close to home.

I grew up on the South Side of San Antonio and attended summer camp in Hunt, Texas, very close to Camp Mystic that was devastated by the flooding. Seeing the damage and hearing stories about people affected by it was a reminder that these floods aren't simply something you see on the news.

They affect real communities and places that many Texans have personal connections to.

But while the Hill Country was dealing with the aftermath, I wanted to take a closer look at what was happening closer to home, and how San Antonio's flood-control system was handling all that water.

San Antonio's Flood-Control System

One of the first things you notice when exploring San Antonio's waterways is how heavily engineered they are.

Some sections look like natural creeks. Others look more like giant concrete drainage channels.

That's not an accident.

San Antonio has a long history of flooding, and the city's flood-control system includes an extensive network of channels, dams and other structures designed to move stormwater away from populated areas as quickly and safely as possible.

Many of the concrete channels are especially noticeable on the South and West Sides of the city.

But some of the most important flood-control infrastructure is much harder to see.

Much of it is underground.

From Flood Disaster to the River Walk

Today, the San Antonio River Walk is one of the city's most recognizable attractions. Restaurants, hotels, shops, bars and tourist boats line the narrow waterway through downtown.

But the River Walk's existence is closely tied to the city's history of flooding.

The devastating flood of 1921 was a turning point for San Antonio. The San Antonio River had repeatedly overflowed, and downtown was particularly vulnerable.

Following the disaster, city leaders began looking for ways to prevent another catastrophic flood.

One proposal would have essentially eliminated the downtown section of the river as people know it today. The river channel could have been covered or paved over while additional drainage infrastructure was constructed to carry floodwaters away.

Instead, architect and planner Robert H. H. Hugman championed a very different idea: preserve the river and turn its banks into a public space.

That vision eventually became the San Antonio River Walk.

What could have been a buried drainage channel instead became one of the most famous tourist attractions in Texas.

The irony is that the River Walk still serves an important flood-control function.

The beautiful waterway that millions of tourists visit each year exists in a channel specifically engineered to manage the river.

The Olmos Dam

Another important piece of San Antonio's flood-control system is the Olmos Dam.

Located just north of downtown near U.S. 281, the dam was constructed following the devastating floods of the early 20th century.

At first glance, it can be difficult to appreciate just how much water the structure is designed to handle.

On a normal day, the area upstream can look surprisingly dry and peaceful.

After heavy rainfall, however, the situation can be dramatically different.

The dam helps control water flowing through Olmos Creek and ultimately into the San Antonio River system. During major storms, the area around it can become a critical part of the city's effort to keep floodwaters away from developed areas downstream.

It's also a good reminder that some of the largest pieces of San Antonio's flood-control infrastructure can sit quietly for months or years, only becoming obvious when the city gets hammered by rain.

A Green Sunfish From the Floodwaters

After looking at the flood-control system, it was time to do what I actually came out there for: fish.

One creek I regularly fish was still extremely muddy. The water looked like chocolate milk, and there was an obvious waterline showing just how high the creek had recently risen.

Despite the conditions, I decided to make a few casts.

The key was getting the bait tight against the bank, where fish could find some shelter from the strong current and muddy water.

Eventually, it paid off.

I hooked into a green sunfish.

It wasn't exactly the bass I was hoping for, but considering the conditions, catching anything was a pleasant surprise.

The fish came from an area that had recently been affected by the flooding, making it a pretty fitting catch for the day.

Inside the Flood Control Tunnel System

From there, I headed to Flood Control Tunnel Inlet Park.

This is where San Antonio's underground flood-control system becomes much easier to appreciate.

A large concrete structure marks the entrance to the flood tunnel. During major flooding, gates can be opened to divert water away from the normal river channel and into the underground tunnel.

The tunnel is enormous.

It was constructed roughly 150 feet beneath downtown San Antonio and stretches for about three miles. The main tunnel is approximately 24 feet in diameter, while the inlet and outlet structures are substantially larger.

When you stand next to the entrance, you cant even really tell what you're looking at. It just appears to be a giant trickling waterfall or another river-art piece. Its difficult to comprehend how much water can be moved through something like this. The system essentially gives San Antonio another pathway for floodwater. The actual tunnel is not visible to the public, but theyve built a park around it.

Flood Control Tunnel Inlet Park. Clever name, I know.

Instead of forcing all of that water through the downtown river channel, some of it can be diverted underground and carried downstream.

That's one of the reasons downtown San Antonio can remain relatively protected even when the region is experiencing serious rainfall.

More Than Floodwater

The flood-control system also leaves its mark on the environment.

At the inlet area, the recent high water was easy to see.

Mud lines on the concrete showed where the water had risen, while vegetation along the shoreline had been stripped away by the rushing water.

There were also signs of wildlife that don't necessarily belong there.

I spotted a suckermouth armored catfish, commonly called a plecostomus, as well as an apple snail. Both are non-native species that have established themselves in San Antonio's waterways.

Flooding can move fish, snails and other aquatic organisms considerable distances, potentially spreading species into areas where they weren't previously established.

For an angler, these post-flood environments can be fascinating places to explore.

They're also a reminder that flooding isn't simply water rising and falling. It can completely rearrange the aquatic environment.

The Flood Tunnel Outlet

The final stop was on the southern end of downtown near Roosevelt Park.

Here, the flood-control tunnel eventually releases its water back into the river system.

The difference between this area and the inlet was immediately noticeable.

The Tunnel Outlet Structure is huge, much larger than the Inlet. The water was considerably clearer, and the shoreline showed a much smaller rise in water level than what I had seen farther upstream.

It also looked like a promising fishing spot.

There was plenty of structure, current and shoreline cover, exactly the kind of things I look for when trying to figure out where fish might hold.

I even found something every angler seems to encounter eventually: somebody else's broken fishing rod and an abandoned soft-plastic lure.

Since I collect discarded soft plastics and recycle them into new fishing lures through my Throw Away Baits project, finding discarded lures was almost as interesting to me as finding a fish.

A River Built to Survive the Rain

Standing beside the outlet and looking at the river, it's easy to forget just how much engineering is underneath and around San Antonio's waterways.

The River Walk, the dams, the concrete channels and the underground flood tunnel are all pieces of a system developed over generations in response to a very real problem.

San Antonio has always been vulnerable to flooding.

The city couldn't simply eliminate the river, nor could it afford to ignore what happened when extreme rainfall sent huge volumes of water through the city.

Instead, San Antonio built around the problem.

Some of that infrastructure is obvious. You can see the dams and concrete channels.

Some of it is hidden underground.

And some of it is disguised as one of the most famous tourist destinations in Texas.

The next time you're walking along the San Antonio River Walk, watching the boats go by and restaurants packed with tourists, it's worth remembering that you're standing in the middle of a massive flood-control system.

And for anglers like me, those same waterways provide something else: a constantly changing environment where a little rain can completely transform the fishing.

After a flood, the water may be muddy, the fish may be scattered, and the conditions may be miserable.

But sometimes, all it takes is one cast in the right spot to prove there's still life in the floodwater.