On Tuesday, Minnesota Department of Natural Resources raised concerns that invasive fish species might be having their way in northern waterways. The department said so as last week, five bighead carp were captured in a river in Minnesota.

After finding the fish in the St. Croix River, the department officials were looking out for more of the fish in the waterway. "This is the furthest upstream invasive carp have been detected in the St. Croix, and is about 7 miles north of the previous point", said the department.

As per the department, there are four species of invasive carp and out of them, silver and bighead carp are threatening the Mississippi River and other native ecosystems. The fish can increase to 60 pounds, which means it can affect the base of the food chain by having large amounts of plankton relied on by native fish.

In the 1970s, Asian carp was introduced in America with an aim that they will control weed and parasite growth in aquatic farms. The US National Park Service said that Asian carp was able to enter into the Mississippi River and they have been found as far north as Minnesota.

The service said, "Experts are worried that if these fish get into the Great Lakes, they may negatively affect the area's $7 billion a year fishing industry".

The discovered fish heads will be sent to the US Geological Survey lab in Columbia, so that it can be determined the age and also, know where the fish originated from.