Fisherman Klaus Hidde wades through the shallow ponds and creeks of Britzer Garten park in Berlin, Germany. Shortly after dawn, he checks his 17 traps. The spoils are rich. As he shakes out the nets, hundreds of crayfish—native to the southern United States and Mexico—tumble into his basket.

The 63-year-old comes from a family of many generations of fishermen. But no one imagined he would practice his trade in the middle of this bustling capital. He was called upon by necessity. Berlin wildlife commissioner Derk Ehlert was desperate.

The Louisiana Crayfish that’s taking over Berlin waterways is an invasive species. It was probably introduced into the German capital’s ecosystem a few years ago when aquarium pets were dumped into local rivers. But the population has boomed. The invader is now crowding out the native “Edelkrebs,” which was already endangered.

As crayfish popped up downtown, city dwellers called officials, reporting alleged “scorpions” and “shrimp” crossing bike paths in Berlin’s Tiergarten park. Overwhelmed by the numbers, Ehlert sought help. He issued Hidde an exclusive license to collect the freshwater crustaceans and sell them to local restaurants.

The new menu item is catching on at the city’s hippest venues. It’s acquired the nickname “Berlin lobster” for its bright red appearance when cooked.

Before proposing putting them onto Berliners’ plates. Ehlert’s office first evaluated their safety for consumption. “We carefully examined the animals regarding possible heavy metals,” he says. Absorption of metals, such as mercury, can be a health concern with shellfish and crustaceans. But the crayfish tested out OK, so that’s when Hidde came out of retirement to take on the American invaders.

“I thought it would be a good idea to help my son’s fishing business and make a few extra bucks,” says the white-haired fisher in olive-green rubber waders.

Hidde says he’s plucked 10,000 from the city’s waters this year so far. In addition to his 17 traps in Britzer Garten, he has another 12 traps in Tiergarten park. A wholesale purchaser buys the critters from Hidde for about $7 a pound. The wholesaler resells them at a Berlin gourmet market hall for $15.50 per pound.

Fish stand owner Matthias Engels says the crayfish are “the right product for people who like sustainability and regional food.”

But is it sustainable if the idea is to eliminate the species? Ehlert says there’s no end in sight. “Where there is a good flow of water, where the animals can migrate, it will be difficult to get rid of them permanently.”