Every spring for the past 30 years, conservationists at the Tuzly Lagoons national park on the Black Sea in Ukraine have been digging shallow channels from the coastal lagoons down to the shoreline, linking the bodies of water together.

The rivulets, which used to occur naturally until industrial agriculture plugged the small rivers that fed them, are a busy through-route for billions of small fish, which winter in the sea then return to the lagoons to breed.

This year, there will be no digging. The beaches are now littered with mines, laid by the Ukrainian army to ward off a Russian offensive. Researchers have had to abandon decades of work, and the consequences for the more than 5,000 herons that feed in the lagoons each spring could be disastrous.

“For 30 years, we organised scientists to do restoration in this area, to save this steppe and support this exchange of water. Now there is no entrance from the Black Sea, no migration of these fish, and the egrets need to eat them,” says Ivan Rusev, the park’s head of research. “It really is a tragedy.”