All summer and into the fall in Upper Manhattan, barbecuers and picnickers flock to the Riverside Park waterfront on Saturdays and Sundays to enjoy the Hudson River views and breezes. Hundreds, sometimes thousands, of people descend on a grassy stretch in the northern part of the park where grilling is permitted. Carne asada and barbecue chicken sizzles, children run, tattooed arms bop volleyballs and couples watch the sun settle over New Jersey.

Then comes Monday morning, which presents a Sisyphean struggle for maintenance workers like Willie Fitzgerald — a weekly encounter with the paper plates, confetti, plastic straws and food scraps that wind up on the grass, along paths and under picnic tables. On a recent Monday, just after noon, Mr. Fitzgerald had already picked up 30 bags of garbage in the park. Now he was using a grabber to pluck plastic cups and popped balloons; he ignored the hundreds of bottle caps embedded in the ground. “Sometimes I pick up a few,” he said, explaining that the caps eluded the grabber’s claws.

Local residents who arrive in the park early on Mondays, before cleanup crews arrive, are greeted with a jarring sight. “At first you think a flock of sea gulls is spread out on the lawn, but it’s paper plates and cups and litter everywhere,” said Nancy Maldonado, 48, who was sitting on a rock by the river. “If this was their house, they would never do this. We need better enforcement.”

Despite such complaints, park officials say their options are limited. They have mostly pursued a strategy of flooding the area with maintenance workers early Monday morning. William Castro, the parks department’s Manhattan borough commissioner, said that despite the recent hiring of scores of new enforcement patrol officers, penalizing parkgoers was impractical. The officers, who carry clubs and mace, focus mainly on loud music and alcohol, which, he pointed out, were the source of even more complaints.