A goldfish presumably flushed down the toilet or illegally released has been captured in the waters of the Niagara River in New York. The Buffalo Niagara Waterkeeper (BNW) is using the opportunity to teach the public a cardinal pet rule: Don’t flush your critters down the toilet, please.

"This is why you should never flush your fish! This 14-inch #goldfish was caught in the Niagara River, just downstream of the wastewater treatment plant. If you cannot keep your pet, please return it to the store instead of flushing or releasing it," said BNW.

The photo is apparently a few years old, but at the time, the hefty goldfish reportedly measured 35 centimeters (14 inches) long. An employee of the US Fish and Wildlife department caught the fish downstream of a wastewater treatment plant. According to BNW, goldfish can survive year-round in these waters, destroying native fish habitat as they thrive. 

"Like tens of millions of other goldfish found in the Great Lakes, our little orange friend most likely ended up in the Black Rock Canal in one of two ways, 1) he or she was directly released into local waterways by a pet owner, or 2) this little fish had the biggest adventure of a lifetime through our city's combined sewer system," said BNW in a statement to IFLScience.

If the goldfish was indeed flushed down the loo, it’s possible combined sewer overflows caused it to end up in the Niagara waterway. Older cities may have issues during heavy rainfall, when sewage and stormwater overflow into waterways before making it to a water treatment facility.

"During rain events, when stormwater enters the sewers, the capacity of the sewer system may be exceeded and the excess water will be discharged directly to a waterbody," notes the New York State Department of Environmental Conservation.

"Discharges from CSO outfalls may contain mixtures of domestic sewage, stormwater runoff, and sometimes, industrial wastewater, including high levels of suspended solids, toxic chemicals, floatable material and other pollutants."

BNW added: "These systems are slowly being improved, but it will take several decades and tens of billions of dollars to fix."

The Great Lakes – which comprise Lake Superior, Michigan, Huron, Erie, and Ontario – contain over 20 percent of Earth's surface fresh water, making up nearly 85 percent of North America's fresh water.

Goldfish (Carassius auratus), native to East Asia, have been kept for centuries. They are resilient creatures – apart from surviving the whoosh and whirlpool of toilets, they can adapt to a variety of water environments. Due to this, they are prohibited in New York for use as bait. In the wild, their colors range from gold to creamy white to olive green. They typically grow between 11.5 and 21 centimeters long (4.5 and 8.5 inches) but can reach lengths of 41 centimeters (16 inches).

"Large and small, hundreds of different invasive species continue to disrupt and cause damage to our Great Lakes," said BNW.

"The story ended well for this fish, but not for our water."