Swelling waterways are part of a healthy ecosystem, experts say
When rivers swell after a rainfall, the fish take notice.
As the current increases, it takes more energy to swim through their regular haunts. So, fish find refuge in parts of the river where it’s quieter—typically, out of the main current and off to the edges, moving into flooded areas that were, until recently, the forest floor.
Moving to this new location has its benefits: Flooded areas tend to have plentiful food in the form of worms, insects and grubs displaced by the rising waters. Plus, the branches and debris provide more places where fish can hide from predators and spawn.
“When flooding occurs in spring, when most fish spawn, the flooding opens up new habitat for spawning, too,” says Robert Bringolf, aquatics professor and associate dean for academic affairs at the University of Georgia Warnell School of Forestry and Natural Resources. “The abundance of food and spawning habitat means that flood years often produce big year classes of fish, which are important for anglers and other predators.”
Record-breaking rains during January and February in the Athens area have pushed rivers near or over flood levels several times. The first two months alone have seen more than 18.5 inches of rain, more than triple the average accumulation for January and February combined.
But still, says Bringolf and associate professor Jay Shelton, flooding is a natural part of the life of a river. While water swelling past a river’s banks might prove risky for people attempting to paddle, it’s a welcome change for the animals living in it.
“In the long run, we tend to see good year classes of species after those floodplains have been inundated the way they are now, and it has positive effects,” says Shelton. “When a wetland floods, a lot of fish use that habitat for nursery areas. Then, when those areas do recede, they actually renourish the river with nutrients and organic matter.”
The one thing that hinders fish as the water churns around them? Sediment, which makes the water look muddy. To fish, it can make it hard to see food or even just navigate through it. The sediment becomes a bigger issue as waterways move through urban areas, where construction and other activity disturbs the ground and causes runoff.
“High water is something they are adapted to, but high turbid water is more of a challenge,” adds Shelton. “The more turbid the water is, the more of an impact it has on them. Turbidity is not a fish’s friend.”
Aquatic connectivity, one of Shelton’s passions, is key to improving overall water quality as well as fish habitat. When water isn’t allowed to flow freely—be it via flood control measures, building levees or dams or other methods—it has a larger effect on turbidity and the overall health of the ecosystem.
“Although floods can create some problems for humans,” says Bringolf, “they are natural and very important for maintaining healthy rivers, not unlike a fire in a forested ecosystem.”