Rangers catching invasive silver carp (Hypophthalmichthys molitrix) as they jump from Fox River, USA. Four species of carp, including this one, were introduced to the US in the 1970s to control parasites and plant growth in fish farms and canals. These carp escaped into the Mississippi river during flooding and rapidly established breeding populations. Silver carp have since spread to rivers in at least 21 states. They can outcompete local species, reproduce rapidly and harm native ecosystems. They also pose a risk to recreational boaters, as disturbance from engines causes them to jump at speed from the water, as seen here.