WARSAW, Poland (AP) — Polish prosecutors on Tuesday pressed animal cruelty charges against the owner of a herd of goats, some of whom died on an island in Warsaw.

Some 60 goats and sheep from a private farm had been sent to an island on the Vistula River last year to help control its lush grass and shrubbery, which was an obstacle to nesting for river birds. The project was supervised by the city's green areas authorities.

But a person who visited the island last week notified ecologists of a number of goat carcasses. City authorities said Thursday that 12 dead goats were found. Some 30 other goats were found alive, but many were in poor condition, according to Dawid Fabjanski of the group Animal Rescue.

If convicted of the charges, the owner could face up to three years in prison, according to Marcin Sadus, a spokesman for prosecutors in the Praga district.

A man who was supposed to watch over the herd told TVN24 he had thrown some goat carcasses into the river on instruction from the animals' owner. Ecologists are warning of potential health hazards to people.

Ewa Rogala, Warsaw Town Hall spokeswoman, said veterinarians have not yet determined the cause of the goat deaths. A check of the island in August reportedly revealed no problems.

Rogala said Animal Rescue has now removed all the goats from the island.