WILMINGTON, N.C. — J. Michael Hutson stood with his neighbors at the edge of the Northeast Cape Fear River on Tuesday morning, watching as its menacing brown waters advanced on their homes.

“This is the nastiest I’ve ever seen it,” Mr. Hutson, 66, said of the tributary of the famed 202-mile river, the biggest in North Carolina. On a sunny summer day, its unobstructed views of a wide blue sky draw people from all over the state, the fishing and boating on its glassy waters an adventure for countless families and friends.

But the Cape Fear River in Wilmington can also be a beast, surging madly from its bed to overtake houses and send residents like Angela Baynes fleeing for higher ground.

Ms. Baynes spent Tuesday morning running back and forth between a river gauge website on her computer and the river itself, watching anxiously as the murky waters swallowed up the boat ramp parking lot and officials urged people to evacuate before the flooding got worse. She and her family had their bags packed and their car gassed up in case they needed to leave.