The savior turning into a villain happens frequently in life and any well thought out strategy for using biological means to counter attack a biological nuisance can go awry as happening in some parts of the US. With all the ingenuity Americans have, a particular species of fish, Asian Carps was imported in 1972 to prevent large scale clogging of water ways due to uncontrolled growth of trouble some Algae. Now it turns that these Carps are suddenly posing grave danger to the very existence of the local species by their greater efficiency in scavenging Algae through their gill rakers attached to the head.
"In November evidence was found that they were present in a canal seven miles from Lake Michigan, and now the fear is that the jumbo-sized aliens will endanger the ecosystem of the entire Great Lakes, squeeze out indigenous salmon, trout and perch by consuming their food sources and threaten the region's $7 billion fishing industry. They are also a serious hazard to the lives of boaters and water skiers because of their tendency to hurl themselves several feet out of the water - with an impact that has been compared to being struck by a bowling ball. The largest have grown to as much as 100lbs in weight".
A single Carp can grow to a huge size and with their fast breeding may choke water bodies all over the US, if not controlled in time. That the US army's service is being sought to tackle this problem speaks itself regarding the gravity of the crisis.