Folks enjoy the hot summer day cooling off in Greenbrier Lake at Greenbrier State Park on Tuesday in Boonsboro, Md. Temperatures reached the upper 90s and are expected to remain high through the week. (Ricky Carioti/The Washington Post)

Omar, the scimitar-horned oryx, couldn’t care less. The crape myrtles love it. But the people in the Washington area may long for October once the week’s blazing weather is through.

The region plunged deeper into its first heat wave of the summer Tuesday, with temperatures in the mid-90s, more of the same expected through Friday and parts of the area facing a dire water shortage because of a failing pipeline.

A huge blanket of steamy air settled over much of the East Coast, prompting heat alerts in Washington, Baltimore and Philadelphia.

Temperatures at Reagan National Airport bounded to 88 by 10 a.m., 92 by noon and 94 by 2 p.m. The high there was 95 just before 3 p.m.

Wednesday is expected to be the same, and Thursday and Friday, with slight moderation by Saturday and Sunday, forecasters said.

At the same time, more than 100,000 people in Prince George’s County faced the loss of water service as utility workers struggled to repair a large water main that serves the southwestern part of the county.

Officials said water could be cut off for up to five days.

On top of that, the Metropolitan Washington Council of Governments issued a Code Orange air-quality forecast for the region for the next three days. Code Orange means the air may be unhealthy for children and adults with respiratory and heart ailments.

The culprit is an unusual summer Bermuda High pressure system that has wandered inland and settled over Indiana, said meteorologist Bryan Jackson of the National Weather Service’s Baltimore-Washington office in Sterling.

“I would say it’s out of the ordinary,” he said. “We’ve got what’s normally a Bermuda High out over the ocean. . . . It’s now centered over the Midwest. It’s just this big heat dome that’s over the northern half of the Eastern U.S.”

But Jason Samenow, chief meteorologist for The Washington Post’s Capital Weather Gang, said the heat wave was pretty standard summer weather. “We’re not talking about threatening any record highs,” he said. “We may or may not touch 100. We’re looking mostly at mid- to high 90s.”

The record for Tuesday is 104, set in 1988. The record for Wednesday is 102, set in 1980.

Across the area, people flocked to pools, where hours were extended, walked on the shady side of the street and perspired freely outside of air conditioning. Mailboxes and fire hydrants were hot to the touch.

But Omar, the oryx at the National Zoo, who has roots in the Sahara, was relaxed.

As a survival mechanism, he can withstand a body temperature as high as 116. He was lounging in the sun Tuesday afternoon while readings hovered in the mid-90s, said animal keeper Gil Myers.

And the hotter the weather, the more the area’s colorful crape myrtles thrive.

“They’re native to temperate and tropical Asia,” said Margaret Pooler, a research geneticist at the National Arboretum. “They’re well adapted to the heat and humidity.”

The mild winter and wet spring helped this year, she said. “Finally, when we’re getting all this heat, they’re just ready to explode,” she said. “When the grass starts to turn brown, and everything else is withering in the heat, the crape myrtles are” in glorious bloom.

Humans, however, were not.

In Washington, near the Mall, vendors sweltered in food trucks, where business was down, and tourists purchased umbrellas for shade and lined up for water and ice cream.

Cathy Bridge, 68, who was visiting the Mall with her grandchildren from Michigan, said, “We knew it was going to be hot, but it’s a little different, the reality of it, walking in it.”

Ruth Simmons, 44, took a break in the shade at the National World War II Memorial. “It’s terrible,” she said. “It’s hard to see everything because the heat makes it difficult to even walk around.”

Downtown, at Farragut Square, “it’s like 105 over here,” Michelle Gerez said from inside Kimchi Taco’s truck.

By about 12:30 p.m., the parking lot at Cameron Run Regional Park in Alexandria was nearly 80 percent full, and families were still arriving in droves. They made a beeline past the batting cages to the pool.

Merary Vasquez, 30, of Washington said the day was so hot that she took off from work and brought her kids to the pool. “It was just so hot,” she said. “They want to refresh themselves.”

The decision seemed to be a hit. “It’s boring at home,” said 3-year-old Jason Vasquez, tugging on his mom’s arm to drag her toward the pool.

Eleni O’Donovan, 41, came to the Alexandria park with her husband and two daughters — 6-year-old Niamh and 4-year-old Norah — ostensibly for a company picnic, though she was eager to let her kids cool off in the water.

“It feels like July finally arrived,” O’Donovan said, sweat starting to trickle from underneath her hat.

O’Donovan said that she was used to a few weeks of heat each summer in her native Boston but that the swampy conditions in Washington often led her and her family to Yards Park, nearer their home.

“I’m not a big fan of the humidity,” O’Donovan said. “The heat doesn’t bother me so much.”

In Fairfax County, as the midday sun glimmered off Lake Barcroft, Sara Photiadis, 23, reclined on the sand by the shore.

“It kind of feels like you’re exercising, but you’re standing still,” Photiadis said. “You’re head is pounding from the unbearable heat.”

She said she swam in the lake to cool off, but the water was 81 degrees.

Wearing a green bikini, Photiadis said she hoped to get a tan before heading to medical school at the University of Virginia in the fall.

“I was just thinking of catching some sun before I’m in the libraries all the time,” Photiadis said.

In Old Town Manassas, construction workers Stan Yoder, 66, of Nokesville and Matt Harris, 31, of Fredericksburg knew how to make sure they weren’t dehydrated: press on a fingernail. If the skin underneath stays white, water is needed. “You need to play it smart,” Harris said.

The heat also took a toll at summer camps around the region.

In Montgomery County, nearly 200 children from the Rockville and Chevy Chase areas were supposed to start their camp days with a 11 / 2-mile hike at Meadowside Nature Center, trudging through wooded trails, taking in birds and other wildlife, and stopping at a creek to look for tadpoles and crayfish.

The temperature-adjusted plan: a brief stop at Cabin John Regional Park, with a day at the pool.

“We change our fun; we definitely add lots of water,” said Bob Sickels, owner of Kids After Hours, which runs nine summer day camps based in schools across the county.

“It’s what we call a three-popsicle day,” he said. With hydration as the goal, popsicles are abundant and counselors preach the rule of eating three. “It’s just a good way to kind of describe, ‘Hey, it’s really hot.’ ”

Jeremy Borden, Stefanie Dazio, Michael S. Rosenwald, Donna St. George, T. Rees Shapiro, Miranda S. Spivack, Bill Turque and Matt Zapotosky contributed to this report.