This time last year, Joe Castro and his staff were repositioning Collin Park Marina to extend the docks into the receding Lake Lavon. Now, Mr. Castro is getting ready to add a temporary bridge because the water line keeps advancing – 24 feet since a year ago.

The marina manager likes this summer's project a lot better.

"We've been wanting water for quite some time," said Mr. Castro, whose marina near Wylie has more than 600 slips. "Now we finally got it, so we're not about to complain."

Lake levels across the region are above normal, and this month's heavy rainfall has boaters thinking the conditions are ideal. But at some lakes – including Grapevine, Lewisville and Ray Roberts – water levels have forced submerged docks to close.

With the July 4 holiday sure to attract boaters, lake officials have issued warnings: Just because the water is higher doesn't make it safer.

"If it were me, I would stay off of it," said game warden Scott Haney of the Texas Parks and Wildlife Department. "The problem is going to be some of those trees and stumps a foot or so below that were 4 or 5 feet above the surface. Someone could hit them in their boats or pulling someone on a tube."

The high water levels have created new shorelines, sometimes hundreds of feet from submerged docks. Local officials warn that boaters traveling on what was once dry land could hit grills or picnic tables.

Or picnic pavilions. At Grapevine's Oak Grove Park, the pavilions were almost completely submerged. Only one public boat ramp, Katie's Woods High Water, remained open Friday on Grapevine Lake.

"It's really crazy," Grapevine parks and recreation spokeswoman Mona Pimentel said. "You can barely see the rooftops of the picnic pavilions."

Public boat ramps at Grapevine Lake have gone underwater in the last week. Visible alongside the new shoreline are the tops of street signs.

Conditions at Lewisville's city-run Lake Park are almost as bad. On Wednesday, Lewisville closed Lake Park for the first time since 1992 and announced it would remain closed for at least two weeks.

The public boat ramps, docks and some roads are under water. Grills and picnic tables barely poke out.

"It makes it dangerous because boaters think because there's water there they can go wherever they want," Lewisville parks director Bob Monaghan said.

Lewisville Lake had risen 4 feet since Sunday. Measuring at more than 530 feet on Friday, the lake is at its highest level since 1992. Last year, the water level never reached 516 feet. The normal level is 522. No other area lake was as high above its normal capacity Friday.

The Army Corps of Engineers – which manages most of the area's lakes – and the state's Parks and Wildlife Department issued news releases Friday warning boaters that higher water levels mean greater danger.

"The current flooding situation is producing even more hazards on the lakes – dangers that can get people into plenty of trouble," the Army Corps warned boaters.

But after enduring drought conditions for several years, marina owners and boaters are enjoying higher waters.

"I'm loving it," said Mike Kranser, commodore of Lewisville Lake Sailing Club. "I personally think the lake is a lot safer being full with the stumps and trees being covered up. Last year, we were worried about running aground. Now we got plenty of water."

The club is based out of Pier 121 Marina in Lewisville, where the water has risen up to the first row of parking spaces. A public dock at the marina is closed, but Pier 121's private marina remains open.

"The fact that we've had plenty high water has been good for business," marina manager Jay Teitelbaum said.

Jennifer Morris, manager of Cottonwood Creek Marina at Lewisville Lake, said her business has been busier than this time last year.

"It gives people the presumption that it's safer because the water is higher," she said, adding that instead, the lakes have become more dangerous.

Officials at area lakes suggest boaters call ahead to see whether their docks of choice remain open. The Army Corps maintains a list of closures on its Web site.

Army Corps spokesman Clay Church said 23 of the 25 lakes managed from the corps' Fort Worth office were above normal water levels Friday. All were still rising.

"To have that many lakes in the flood pool is unusual," he said.

Still, Army Corps officials said the situation does not pose a concern for major flooding.

"Our lakes are doing their jobs," Mr. Church said. "We have a flood pool area to hold water, and that's what we're doing."

Staff writer Stella M. Chávez contributed to this report.