Aquatic Invasives

Water Invaders

Aquatic invasives live in and around lakes, waterways and wetlands. Many “hitchhike” from one body of water to another on watercraft, bait buckets and other recreational gear. Others arrive when people illegally empty bait buckets or aquariums into lakes and waterways.

Asian Clam Corbicula fluminea

Where It's From & How It Got Here

Southeast Asia likely from illegally emptied aquariums and bait buckets or wet recreational gear

What It Looks Like

2-inch-long brown-to-black triangular shell with distinctive elevated ridges; deep-purple to white inner shell

What It Does

They live up to nine years and breed, grow and spread quickly, stealing habitat and food from native clams. They prefer shallow, quiet waters with sandy bottoms and are in many DuPage lakes and rivers.

 

Chinese Mystery Snail Cipangopaludina chinensis

Where It's From & How It Got Here

Asia likely from illegally emptied aquariums and bait buckets or wet recreational gear

What It Looks Like

2-inch-long light to dark olive-green shells; deep purple to white inner shell

What It Does

They eat microscopic plants and animals and can transmit parasites and diseases harmful to humans. They're common in DuPage lakes, wetlands and backwater areas of rivers, where they steal food and habitat from native snails and clog water-intake pipes.

 

Common Carp Cyprinus carpio

Where It's From & How It Got Here

Brought from Europe in 1800s and widely distributed by the federal government as a food fish

What It Looks Like

Relatively broad, heavy-bodied; variable color; toothy spine; 1 – 2 feet long and 1 – 8 pounds (but can reach 40 pounds); two rounded deep lobes on tail; sometimes has two barbels at corners of mouth

What It Does

Carp grub for food along the bottom, churning up nutrients and sediment as they go, particles that prevent sunlight from reaching plants and animals that need it to survive. They breed quickly and are widespread in lakes, ponds, wetlands and rivers.

 

Goldfish & Koi Carassius auratus auratus & Cyprinus carpio

Where It's From & How It Got Here

Illegally dumped from aquariums and backyard ponds

What It Looks Like

Goldfish are closely related to the common carp; koi are common carp bred for color. Hybridization between species within the carp family is not uncommon.

What It Does

These are some of the most widespread aquatic invasives in the U.S. Goldfish are particularly well-adapted because they eat a variety of foods, tolerate poor environments and reproduce prolifically. 

 

Red Swamp Crayfish Procambarus clarkii

Where It's From & How It Got Here

From Gulf Coast and Mississippi River basin to southern Illinois likely from illegally emptied aquariums and bait buckets (and possibly restaurants)

What It Looks Like

Dark red with raised bright red spots and a black wedge-shaped stripe on the top of its abdomen; grows to 8 inches long

What It Does

Red swamp crayfish make up the majority of farmed crayfish consumed worldwide. In wild areas they've invaded, they steal habitat and food from native crayfish and lower amphibian populations by eating their eggs and young and competing with adults for habitat. 

 

Round Goby Neogobius melanostomus

Where It's From & How It Got Here

Black Sea from ballast water in commercial freighters

What It Looks Like

Up to 10 inches long; distinct black spot on first dorsal fin

What It Does

These bottom-dwellers are voracious eaters that easily out-compete native sculpin and logperch and can decimate populations of native game fish by eating their eggs. 

 

Rusty Crayfish Orconectes rusticus

Where It's From & How It Got Here

Middle Ohio River Basin likely from illegally emptied aquariums and bait buckets

What It Looks Like

Up to 4 inches long; distinctive rusty spots on sides

What It Does

These aggressive crayfish steal habitat and food from native species and have rapidly expanded their range by interfering with the reproduction of native species.

 

Weather Loach Misgurnus anguillicaudatus

Where It's From & How It Got Here

Eastern Asia likely from illegally emptied aquariums

What It Looks Like

Eel-like body up to 9 inches long; small narrow mouth surrounded by six barbels

What It Does

Weather loaches live along the silty bottoms of low-gradient, shallow waters, often in submerged plant beds, where they steal habitat and food from native fish.

 

Zebra Mussel Dreissena polymorpha

Where It's From & How It Got Here

Russia from ballast water in commercial ships

What It Looks Like

1- to 1.5-inch-long striped shells

What It Does

Zebra mussels are now in over 25 states; control costs in the Great Lakes alone is $100 –$400 million annually.

Just one adult can filter the microscopic plants and animals from 1 quart of water in one day; one colony can clear an entire lake. This leaves little food for small native animals, such as zooplankton and small fish. As a result, populations of larger fish, which feed on the smaller fish, also decline. In some areas zebra mussels clear the water to such an extent that walleye and other light-sensitive fish must move to deeper waters.

The increased sunlight also means aquatic plants can grow denser at greater depths, which creates habitat for small fish but prevents larger predators from finding food. The dense beds also cause problems for boaters and anglers. 

As zebra mussels die, their decaying bodies create foul odors, and their sharp shells pile up on shorelines.

 

Common Reed Phragmites australis

Where It's From & How It Got Here

Europe likely accidentally in ballast water from ships

What It Looks Like

2- to 2.5-inch-wide grey-green leaves 8 – 15 inches long; distinctive purple-brown plumes at tips of stalks appear late July; grows 6 – 15 feet tall with 80 percent of mass underground

What It Does

Also called phragmites, this perennial overtakes wetlands and shorelines, creating tall, dense stands. It primarily spreads by rhizomes (horizontally growing stems at or below the surface) and root fragments. Each rhizome can spread over 60 feet and grow over 6 feet tall per year. Roots and rhizomes can accumulate in the soil over 6 feet deep. 

 

Curly Leaf Pondweed Potamogeton crispus

Where It's From & How It Got Here

Eurasia, Africa and Australia from hobbyists in the mid-1880s for use in aquariums

What It Looks Like

3-inch-long oblong reddish-green leaves with wavy, fine-toothed edges; flat reddish-brown stems 1 – 3 feet long

What It Does

The plant spreads via seeds and burrlike winter buds, which move along waterways. New plants form under the ice, making it one of the first invasives to emerge in spring. Dense mats prevent sunlight from reaching native plants and animals below and create problems for anglers and boaters. As the plants decay, they release nutrients into the water that contribute to algal blooms and create foul-smelling messes along the shore.

 

Eurasian Water Milfoil Myriophyllum spicatum

Where It's From & How It Got Here

Eurasia, Africa and Australia from hobbyists in the mid-1880s for use in aquariums

What It Looks Like

Slender, whorled stems and threadlike leaves, each with 12 to 21 pairs of leaflets; tiny four-petaled or petal-less flowers that grow above the water; four-jointed nutlike fruits

What It Does

The plant is spread by fragments that hitchhike on recreational gear and wildlife. Just one 2-inch fragment can start a new colony. Dense mats prevent sunlight from reaching native plants and animals below and create problems for anglers and boaters. 

 

Flowering Rush Butomus umbellatus

Where It's From & How It Got Here

Eurasia, Africa and Australia from hobbyists in the mid-1880s for use in aquariums

What It Looks Like

Narrow 3-foot-long above-water leaves with triangular cross-sections; three-petaled flowers with three white or pink sepals in distinctive flat-topped sprays atop tall stalks

What It Does

Flowering rush spreads by rhizomes (horizontally growing stems at or below the surface) and root pieces. It's often mistaken for a native rush because it's difficult to identify when it's not flowering.

 

Purple Loosestrife Lythrum salicaria

Where It's From & How It Got Here

Europe and Asia in the 1800s likely from gardeners or ballast water from ships

What It Looks Like

4  – 7 feet tall with up to 30 purple-flowered spikes 

What It Does

Each plant can produce 2.5 million seeds in one year. This hardy, aggressive perennial takes over wetlands and moist soils but offers little food value to wildlife. Unsuspecting people often pick and spread its flowers.

 

Reed Canary Grass Phalaris arundinacea

Where It's From & How It Got Here

Gulf Coast and Mississippi River basin to southern Illinois likely from illegally emptied aquariums and bait buckets (and possibly restaurants)

What It Looks Like

Smooth, erect flowering green stems 3 – 7 feet tall; leaves 0.5 inch wide and 4 – 8 inches long

What It Does

One of the most aggressive invasives in the Midwest, this plant spreads via rhizomes (horizontally growing stems at or below the surface). It forms dense stands in wet meadows and marshes and around rivers as well as in prairies and woodlands.