Some very small creatures are forcing some big changes in a popular section of Whistler, B.C., as an annual migration begins to peak.

The resort municipality has closed the Lost Lake access road, a parking lot and the events lawn, and says other closures are possible as thousands of western toadlets make their trek from the lake into the surrounding forest.

The dime-sized amphibians are native to British Columbia and listed as a species of special concern.

They breed in the lake, where tadpoles mature, then spend most of their time in the forest, meaning as many as 40,000 of the tiny toads have to hop across beaches, trails, lawns and roads during the August migration.

The municipality says busy Lost Lake beach and the beach lawn are still open but could be closed if high numbers of toads start hopping in that direction.

The newly hatched Western Toad is not much bigger than a human fingernail. (CBC)

Tough to see

Other areas around the lake are still open, but visitors are advised to look for "active migration zone" signs and watch where they ride or step because the toadlets are tough to see and can be easily crushed underfoot.

The creatures have been included in Whistler's monitoring program since 2005 as the municipality focuses on species that offer insight into the health of area ecosystems.

The municipality says western toads are an important part of the Lost Lake environment because the tadpoles feed on residue in the lake, keeping the water clean.

"Monitoring the stages and development of the tadpoles throughout the summer enables [environmental technicians and volunteers] to proactively prepare for the migration and focus on public education," the municipality says in a news release.