All 2,800 sites in 25 provincial campgrounds that can be reserved online are fully booked. (CBC)

Alberta's campgrounds are filing up fast for the August long weekend, and those without reservations might be unhappy campers.

All 2,800 sites in 25 provincial campgrounds that can be reserved online are fully booked, Alberta Parks spokeswoman Camille Weleshuk said. However, if people change their minds about camping and cancel their reservation, those spots would become available online.

Reporting from a campground in Bow Valley Provincial Park west of Calgary, CBC News reporter Tom Spears said Friday morning campers had told him they had reserved a spot online months ago, and while some spots were available on a first-come, first-serve basis, those were expected to be snapped up by early afternoon.

"Camp operators are expecting a busy weekend," Spears reported. "No rain or snow in the forecast, and no fire bans or trail closures."

Another 38 provincial campgrounds take reservations by phone, and an additional 200 campgrounds fill up on a first- come, first-served basis.

Since the online reservations system was launched on May 1, 50,000 reservations have been made.