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The Consequences Of No One Picking Up Their Dog’s Poop Are Horrifying

New York just endured a substantial batch of snow — if not exactly the blizzard that was advertised. That set it up for the unfortunate defrost, leaving the city’s sidewalks covered in piles of dog crap people didn’t pick up.

This inevitability prompted a bit of speculation on my part: What would happen if nobody in New York picked up after their dog? How weird would it get and how fast? This hypothetical might seem far-fetched, but not picking up after dogs is somewhat common. A 1999 study of Chesapeake Bay area residents estimated 41 percent of people who walked their dog in public rarely or never picked up after it.

Let’s take this step by step:

First, how many dogs are in New York? I’m going with a 2012 estimate from economists at the New York City Economic Development Corp.: 600,000 dogs.

So, how much do they poop?

I thought about trying to find how much dog food is sold in New York, figuring inflows equal outflows. But that seemed imprecise. After a bit of digging, I uncovered some actual scholarship: A 1999 paper from the Watershed Protection Techniques journal indicates that dogs poop about 0.32 pounds per day (I assume there’s substantial variation between breeds). Seems about right.

Multiplying the number of dogs by that poop rate gives us 96 tons dropped each day in New York City.

How much is that exactly? Repeated attempts to Google the density of dog poop went unrewarded, and while I’m typically down to conduct IRL measurements, I’m not in this case. However, given that New York has 12,750 miles of sidewalk, that comes out to a pound of dog crap for every 350 feet of sidewalk every day (if we assume they only relieve themselves on sidewalks). After a week, that’d be a pound every 50 feet.

Besides the aesthetic problems — or improvement, if we’re talking Times Square — there’s a public health issue. Dog shit has 23,000,000 fecal coliform bacteria per gram, so that’s an additional 2 quadrillion coliform bacteria added to the sidewalks each day, give or take, which can’t be healthy. Studies of three midsize cities found that 10 to 50 percent of bacteria in air samples was derived from dog waste.

There might be environmental effects, too. Not that the Hudson River is exactly a paragon of cleanliness, but microbiologists suggest that dog poop can be a big polluter. The Environment Protection Agency says domestic animals — which includes cats, which at least have the decency to pick a place and stick with it — contribute nitrogen and phosphorous to ground and surface waters, and poop from pets can contribute to eutrophication and closure of shellfish beds.

Indeed, even if we let poop pile up, we’d really be in the shit when it rains. New York relies — in most areas — on a combined sewer system, which means that storm drains and residential waste water all go to the same pipe, which is then treated at one of the city’s wastewater treatment plants. The city treats 1.3 billion gallons daily and can remove 85 to 95 percent of pollutants when everything is going swimmingly.

The city’s treatment plants can handle about double the normal flow. But if they reach their limit, there’s a “combined sewer overflow” (CSO), which is when the stuff they can’t handle gets dumped into rivers. The city says plants can capture more than 80 percent of a CSO, but we can suppose about a fifth of the mess is still getting in the river. Factor in 96 tons of dog crap every day, and the East River would be slightly more disgusting than usual.

What would happen if people didn’t pick up their dog’s crap? Pestilence, plague, pollution, declining property values (I assume) and possible environmental damage. In reality, if 41 percent of New Yorkers didn’t clean up after their dog (as was found in the Chesapeake Bay study), 39.3 tons of dog crap gets left on the sidewalks each day — a little less than the weight of a subway car on the F train.

The moral of the story? First, pick up your dog’s poop, even in the snow. Second, the way New York handles its wastewater is fascinating. Third, you get really strange ads for the next couple of days if you repeatedly search for the density of dog poop.

Walt Hickey was FiveThirtyEight’s chief culture writer.