In Whistler, British Columbia, about 50 miles north of Vancouver, there is a body of water known as Lost Lake, where tens of thousands of tiny, dime-sized toads breed every year. Known as western toads, the amphibians then migrate from the lake to surrounding forests. There are an awful lot of hiking and biking trails in their way—each one a fresh, harrowing hazard to life and limb.

In recent years—including this year—authorities have been blocking off trails and even closing an entire road in an attempt to protect the little hoppers. The migration is long, though, beginning in late July and ending in August or even September, meaning that authorities’ best efforts don’t always work.

“On the busy holiday weekend, many trail users were observed not obeying the signs—even with volunteers standing nearby—and blew by gates on their bikes,” the CBC reported Monday.

The toads are extraordinarily exposed to danger from humans. Their sensitive skin that can be damaged by the oils in one’s hands, and they are so tiny that one is not likely even to notice one underfoot (or under tire, for that matter).

But they do have numbers on their side and most of the toads are expected to survive the journey. The species is considered vulnerable but not endangered, and has been getting bigger in recent years. A record number of breeding pairs were spotted this year.

“The toads,” the municipality of Whistler said on its website last month, “are on the move!”