Rescuers say the water in Colorado can be more dangerous than it looks to the untrained eye.

It's "swiftwater season" in Colorado for first responders. Members of Boulder Fire Rescue began training for rescues Tuesday.

"People don't really understand how powerful the river really is," said firefighter Brad Lupher. "You can get taken into the water fast and not be able to get back out."

Emergency responders in Boulder say they experience a spike in 911 calls about water incidents this time of year. People don't seem to be getting the message about how dangerous the water could be, Lupher said.

"I think the main problem is people don't know their limits," Lupher said. "It can get really fast and really dangerous and you can get into trouble instantly."

An adult can be swept away in a matter of seconds. The department has responded to two rescues already this season, according to Lupher.

"With the last rescue, someone went and bought a floating mat that's made for a swimming pool and they decided to go down in the creek," he explained.

Snowmelt typically causes an increase in water levels across Colorado. Officials say higher levels can increase risks for those who venture in the water because the flow is powerful and there is a lot of debris.

"There's a lot of rocks and branches and things like that that you can't see because they're just below the surface," Lupher said.

He said it's a reminder of how quickly conditions can change this time of year.

A woman died after a boating accident on the Colorado River in Eagle County on Monday afternoon.

RELATED: Woman dies after getting trapped in Colorado River rapid

The Eagle County Sheriff's Office says the woman in her 30s was part of a group riding boats and kayaks in the river near Bond. Her boat got stuck on a raft that was already pinned to a rock. Others in the group swam to safety, but she was trapped, investigators said.

The woman was later pulled from the river and was unresponsive.

Water levels in Boulder Creek are average right now, according to the USGS. Officials expect levels to double by next week as the Barker Reservoir reaches full capacity.

Water levels in Clear Creek are also rising. The creek went from about 300 cubic feet per second to 900 cubic feet per second in one week's time.