WHITE RIVER JUNCTION — Lynnea Butterfield couldn’t wait to go swimming.

The 5-year-old was first in line outside the gates of the Sherman Manning Aquatic Facility in White River Junction about 10 minutes before open swim hours were set to start at 1 p.m. Monday.

“Too hot,” Lynnea said about the temperature, which was in the mid-90s, as she and her mom, Kathryn Ward, waited by the gate.

The National Weather Service issued extreme heat watches and advisories for multiple counties in the Twin States — including Windsor and Orange counties in Vermont and Grafton and Sullivan counties in New Hampshire — warning that “potentially dangerous heat is anticipated for Monday and Tuesday.”

On Friday, the Vermont Department of Health issued a news release warning people that “high heat can increase the risk for dehydration, muscle cramps, headache, nausea, fainting, or even heat stroke.”

Older adults, people with disabilities and those with chronic health conditions are at especially high risk of developing “severe heat illnesses,” the release said.

“It is important to take the proper steps to keep yourself and loved ones safe during extreme heat,” Robert Buxton, the director of New Hampshire’s Division of Homeland Security and Emergency Management, said in a Monday news release.

Those include staying indoors to avoid the sun, not leaving children or pets alone in vehicles and staying hydrated. New Hampshire residents can call 211 to find the cooling center nearest to their homes.

The heat caused a slight change in schedule at the pool in White River Junction, with children enrolled in camp through the Hartford Recreation and Parks Department spending more hours at the pool, head supervisor Liam Clark said. Open hours — where residents from any town can stop by to swim — were scheduled for 1 to 7 p.m. (Day passes are $3 for Hartford residents and $5 for nonresidents.)

“My glasses fogged up this morning, but it wasn’t terrible,” Clark said about the heat.

Every 45 minutes on hot days, pool staff urge swimmers to drink water and suggest they reapply sunscreen, Clark said. He noted that the pool has a free sunscreen dispenser for those who need it.

“The pool is still cool enough that it’s refreshing,” assistant supervisor Ava Thorburn said. On days like Monday and Tuesday, the pair expected they’d see as many as 200 people. “We get pretty busy.”

Monday was the third day Lynnea and Ward, of White River Junction, have spent at the pool since it opened June 16.

“It’s a great place to come and hang out,” Ward said.

The Hartford Library in Hartford Village also is available for people in need of a place to cool off. Twenty adults and two children had already dropped by as of noon Monday, assistant librarian Deborah Milne said. The library is open from 9 a.m. to 6 p.m. during both days of the heat wave.

“We have a great heat pump system,” she said in an interview at the library.

While no one had dropped by particularly for the air conditioning, Milne expected that to change as the afternoon went on and into Tuesday. When the heat rises, “the computers all of a sudden become popular,” she said.

The Department of Health maintains a list of cooling stations in Vermont. A full list of locations is online at healthvermont.gov/environment/climate-health/hot-weather.

Upper Valley cooling sites

■Bugbee Senior Center, 262 N. Main St., White River Junction

■Hartford Library, 1587 Maple St., Hartford Village

■West Hartford Library, 5311 Route 14, West Hartford

■Norwich Public Library, 368 Main St., Norwich

■Thompson Senior Center, 99 Senior Lane, Woodstock

■Windsor Resource Center, 1 Railroad Ave., Windsor

■West Windsor Town Hall, 22 Brownsville-Hartland Road, West Windsor

■Latham Library, 16 Library Road, Thetford

■Greater Randolph Senior Center, 6 Hale St., Randolph

■Kimball Public Library, 67 N. Main St., Randolph

Additional locations are available on the New Hampshire side of the Upper Valley. Lebanon has opened four cooling shelters Monday and Tuesday:

■Lebanon Public Library, 9 E. Park St., Lebanon

■Kilton Library, 80 Main St., West Lebanon

■Upper Valley Senior Center (older adults only), 10 Campbell St., Lebanon

■Lebanon Airport Terminal Building, 5 Airpark Road, West Lebanon.

In Enfield, residents can find relief at the Enfield Public Library/the town offices at Whitney Hall, located 23 Main St., and the Public Works facility, located at 74 Lockehaven Road.

Claremont has also designated the Claremont Savings Bank Community Center at 152 South St., as a cooling shelter for Monday through Wednesday.

Liz Sauchelli can be reached at esauchelli@vnews.com or 603-727-3221.