NEW ORLEANS — It's a beloved century-old Carnival season tradition in New Orleans — masked riders on Arvin Robertslavish floats fling strings of colorful beads or other trinkets to parade watchers clamoring with outstretched arms.

It's all in good fun but it's also a bit of a "plastics disaster," says Judith Enck, a former Environmental Protection Agency regional administrator and president of the advocacy group Beyond Plastics.

Carnival season is at its height this weekend. The city's annual series of parades began more than a week ago and will close out on Tuesday — Mardi Gras — a final day of revelry before Lent. Thousands attend the parades and they leave a mess of trash behind.

Despite a massive daily cleanup operation that leaves the post-parade landscape remarkably clean, uncaught beads dangle from tree limbs like Spanish moss and get ground into the mud under the feet of passers-by. They also wash into storm strains, where they only complicate efforts to keep the flood-prone city's streets dry. Tons have been pulled from the aging drainage system in recent years.

And those that aren't removed from the storm drains eventually get washed through the system and into Lake Pontchartrain — the large Gulf of Mexico inlet north of the city. The nonbiodegradable plastics are a threat to fish and wildlife, Enck said.

"The waste is becoming a defining characteristic of this event," said Brett Davis, a New Orleans native who grew up catching beads at Mardi Gras parades. He now heads a nonprofit that works to reduce the waste.

One way of making a dent in the demand for new plastic beads is to reuse old ones. Parade-goers who carry home shopping bags of freshly caught beads, foam footballs, rubber balls and a host of other freshly flung goodies can donate the haul to the Arc of New Orleans. The organization repackages and resells the products to raise money for the services it provides to adults and children with disabilities.

The city of New Orleans and the tourism promotion organization New Orleans & Co. also have collection points along parade routes for cans, glass and, yes, beads.

Aside from recycling, there's a small but growing movement to find something else for parade riders to lob.

Grounds Krewe, Davis's nonprofit, is now marketing more than two dozen types of nonplastic, sustainable items for parade riders to pitch. Among them: headbands made of recycled T-shirts; beads made out of paper, acai seeds or recycled glass; wooden yo-yos; and packets of locally-made coffee, jambalaya mix or other food items — useful, consumable items that won't just take up space in someone's attic or, worse, wind up in the lake.

"I just caught 15 foam footballs at a parade," Davis joked. "What am I going to do with another one?"

Plastic imports remain ubiquitous but efforts to mitigate their damage may be catching on.

"These efforts will help green Mardi Gras," said Christy Leavitt, of the group Oceana, in an email.

Enck, who visited New Orleans last year and attended Mardi Gras celebrations, hopes parade organizers will adopt the biodegradable alternatives.

"There are great ways to have fun around this wonderful festival," she said. "But you can have fun without damaging the environment."