Blue crabs, those tasty symbols of the salty Chesapeake Bay, are showing up in the freshwater of the James River in downtown Richmond.

A lot of people don't realize it -- or they heard the story for years and didn't believe it -- but crabs often migrate here in summer when the river gets low.

"We've been getting a bunch of calls here lately," said Gary Martel, fisheries director for the state Department of Game and Inland RT-D FIRST Fisheries. "People are wading and fishing and seeing them and saying, 'Hey, what goes? There's blue crabs in Richmond.'"

For people who live along the salt marshes of coastal Virginia, crabs and crabbing are part of summer. For some Richmonders, they are a fascinating oddity.

"Crabs kind of weird me out. . . . They look like aliens or something," said fly fisherman Michael Kaplan of Richmond.

Chris Hull of Henrico County likes to swim and snorkel in the James with his wife and four children. He said the first time he told his wife he saw crabs, about six years ago, she worried that he might have hit his head on a rock.

"She said, 'Crabs don't live in the rapids,' and I said, 'Yes, they do,'" he said.

The crabs may come to the river looking for freshwater clams to eat or for the higher oxygen levels that rapidly moving water offers, said Michael Seebo of the Virginia Institute of Marine Science.

It's not unusual for crabs to move into freshwater, said Seebo, a marine scientist. They can live in freshwater but can't reproduce in it.

In winter, the James River switches from salt water to freshwater well below Hopewell, more than 40 miles below Richmond. But during dry summers, that salt water -- and the crabs in it -- move several miles closer to Richmond.

The river is slow and tidal until the first set of rapids, around the Mayo Bridge at 14th Street. Crabs, those zippy little sideways swimmers, can shoot upriver through rapids when the water is low, as it is now.

They tend to concentrate in a roughly quarter-mile stretch between the Mayo Bridge and Brown's Island.

The crabs seem to be particularly abundant this summer. "You can't hardly walk 20 feet without seeing one," said angler Tye Krueger of Richmond.

If you want to do more than watch the crabs, you can legally catch up to a bushel a day if you aren't selling them. Hard-shelled male crabs must have shells at least 5 inches long. Most of the crabs at the river are male. Health officials suggest cooking the crabs well to kill bacteria.

The crabs typically show up in midor late summer and move out by October, said Ralph White, manager of James River Park. "It's a fascinating thing to see," he said. "This is the time and the place. Don't try this in December, and don't try it in high water."

Contact Rex Springston at (804) 649-6453 or rspringston@timesdispatch.com.