A few weeks ago, the Illinois Department of Natural Resources (IDNR) received a notification from an HOA on Ginger Creek that they had observed a new invasive species within their lakes: Hydrilla Verticillata, commonly referred to as just “Hydrilla.” This is the first reporting of this invasive aquatic plant in the Salt Creek watershed. Hydrilla is a nasty invasive plant that originates from Asia. It is used commonly as an aquarium plant and was introduced from people dumping aquariums with Hydrilla into local waterways where it has flourished.
Figure 1: The current extent of invasive Hydrilla. The aquatic plant was first introduced in Florida and has spread aggressively from there (https://www.eddmaps.org/).
Hydrilla is problematic because it grows so exceptionally well here. It requires very little resources from its environment to grow and can outcompete natives in poor habitat. It also regrows from broken up fragments so manual collection methods tend to only increase its dispersal, much like the Hydra from Greek mythology. It also produces tubers that grow in the bottom of lakes and rivers that allow it to overwinter and survive other hardships that would kill off other native plants. Hydrilla is very tolerant of saline waters, which is something that our watersheds are grappling with right now. Salt concentrations in the watersheds are increasing over time and harming native aquatic life. This emerging pollutant, combined with an invasive species that isn’t harmed by salinity, compounds the danger of Hydrilla.
Figure 2: Tubers that grow on the roots of Hydrilla. These tubers are small and often white. They enable the plant to survive harsh conditions. Image credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Hydrilla’s explosive growth chokes out other species to the point that no other aquatic plants can grow. This means there is not native foods for fish and invertebrates. It clogs up rivers and lakes, and the extreme growth affects the pH and dissolved oxygen levels in lakes and rivers leading to fish kills. Given the potential this plant has for expansion, the severity of issues it creates, and the difficulty in eradicating it, finding it early and keeping it out of our watersheds is very important.
INDR has been investigating the presence and expanse of Hydrilla in the watershed, and last week we met three IDNR employees and went out on a hunt to see if we could confirm the presence of Hydrilla closer to the Salt Creek mainstem. We were armed with waders and double headed rakes attached to a length of rope. The method of searching for Hydrilla in lakes is a strange sight if you are unfamiliar with the practice. We stood ashore and launched the rakes out into the water, waited a moment for them to sink to the bottom, and then pulled them in. As the rakes scour the bottom of the lake, they drag up plants, trash, mud, and any other debris that gets caught in the mass of muck. Then we start picking through the mess and pulling out all the plant material. We look for plants that meet the description for Hydrilla and hope that we do not find any. After we scour one section of the bank, we move a little way along and start over.
We maintained the search for the better part of the day. Our small team covered several lakes, and searched along Salt Creek and up Ginger Creek. Thankfully, it was a boring day. We did not find any signs of Hydrilla, although, as it is late in the season, it could very well be hidden. While there is a good chance that Hydrilla has not migrated out of Ginger Creek and into Salt Creek yet, the reality is we searched only a small area, and more surveillance will be needed. IDNR is continuing to monitor the stream reach, and are planning to apply for grant funding to tackle the invasive plant.
Invasive infestations are substantially easier to manage when you catch them early. It is much more difficult to remove thousands of plants across miles of rivers and from within dozens of lakes, than it is to remove one stray plant that has snuck into the river on a boat. However, it is vastly more difficult to find these invasives until they are well established. One can only be so thorough when throwing a rake into a lake. Even a small colony of plants is easy to miss until it becomes a nuisance. Short of going in with a team of scuba divers and searching every square foot, it’s hard to say with utter certainty that there is no Hydrilla present downstream.
Figure 3: Hydrilla Verticillata. Invasive aquatic plant with long slender stems that can reach up to six feet in length. Notice the whorls of leaves moving along the stem. Leaves are in clusters of 5. Image Credit: Raghavan Charudattan, University of Florida, Bugwood.org
Hydrilla can be identified best by its leaves. They are typically present in whorls of five or more along the stem, which is long and slender. The leaves also have tiny serrations and can feel rough on you skin when you pull the leaves between your fingers. There is another plant, Elodea, which looks very similar and is native. Elodia lacks the leave serrations, and has only three leaves in each whorl. To help prevent the spread of invasive species, make sure you clean your boats, waders, and other aquatic gear after every trip. Do not dump aquarium water, fishing bait, pet fish, or anything else into local rivers and streams. If you think you find Hydrilla or other invasive species, report it to the appropriate conservation agency!
Figure 4: A large mass of Hydrilla attached to a boat trailer. When Hydrilla overgrows a lake, it is easy for it to catch on aquatic equipment. If not cleaned off, it will spread to other lakes and rivers (https://seagrant.noaa.gov/north-carolina-coastal-collaborations-focus-on-invasive-hydrilla/).
