SAN FRANCISCO (AP) — Dam experts say the collapse of spillways at the nation’s tallest dam this winter has raised alarms nationally because there appeared to be no warning that the spillways were about to fail.

Speaking to reporters for the first time Thursday, an independent group of dam safety experts say they would’ve expected warning signs leading up to the collapse.

Most dam emergencies happen during flooding, but the spillways at California’s Oroville Dam began breaking up suddenly in February under relatively small amounts of water.

Authorities evacuated nearly 200,000 people after both flood-release spillways started falling apart. The expert team is conducting its own probe into the failure.

Investigation leader John France says dam professionals nationally want to know how the collapse of Oroville’s main spillway came as such a surprise.