Portland's dog owners seem to be doing a better job these days of scooping up their pets' poops.

But the city's Public Works Department is not exactly jumping for joy.

That's because, while it's much easier to navigate the city's sidewalks, there is still a whole lot of doggy doo ending up in the city's storm drains and waterways, all wrapped up nicely in plastic bags.

"They go all through the trouble of picking it up," said John Emerson, the department's wastewater coordinator. "Then, rather taking it home with them, they'll flip it into the storm drain."

Those left to clean the resulting mess say dog walkers probably figure the bags of poop will go directly from the storm drains to the city's sewage treatment plant. But about half of the city's storm drains lead instead to places like Capisic Brook, the Presumpcot River, the Fore River and Casco Bay, they said.

"Dog bags have been a particular problem as of late," Emerson said.

But this pet peeve also represents a much bigger problem facing the city and Maine's other urban centers.