Bringing along a few pieces of day-old bread to feed the ducks at a local pond seems innocent enough, but a biologist with Newfoundland's Memorial University says you might want to think twice next time you go.

"It's junk food for ducks," said Dr. Steve Carr in an interview at Burton's Pond, a popular spot on campus that attracts many ducks — as well as well-meaning visitors who don't know the harm that breadcrumbs can do.

According to Carr, the worst thing to feed a duck is a slice of bread.

Here are the reasons why.

1. Bread makes ducks fat

"[They're] empty carbs. Giving large amounts of bread is exactly like feeding your children nothing but bread," Carr told the St. John's Morning Show.

"It will get them fat and obese, but won't give them proper nutrition."

2. Ducks become dependent on us

Carr said it's dangerous to feed bread to ducks for a number of reasons, but it's particularly dangerous for ducklings.

"They don't learn proper foraging behaviour. If it's simply every time they see a human they go up and you spread bread in front of them, they won't learn," he said.

"You'll see some of them standing on their heads and going down to the bottom and trying to pull up plant life," he said.

3. Bread can cause diseases

Besides nutritional problems, Carr said overuse of bread can lead to specific diseases that can become problematic in any pond.

Carr said when fecal material goes into the pond, it's a source of botulism bacteria that can spread among the ducks.

"It can wipe out an entire waterfowl colony," Carr said.

"The second thing is, a lot of people will bring down bread that has gone bad. And when it goes bad, it has that little green mould in it, and that mould actually causes specific diseases in ducks. It causes lung diseases, so it's not just nutritionally bad — it can just kill them outright."

4. It can hurt the pond, too

Carr said most of the bread that people feed ducks ends up not being consumed, adding anything not eaten will sink to the bottom of the pond, rot and potentially change the ecosystem.

Empty carbs … like feeding your children nothing but bread. - Steve Carr, biologist

"Folks will say, 'We only go down once a month, and we just feed one loaf of bread and that can't harm anything.' But when you think about it, if there are a thousand families, that's something like 30 loaves of bread a day," he said.

"It will rot. The algae love it, it kills the birds, kills the other plants, there's no oxygen left. The fancy biological word is eutrophication — you've got a dead pond. They go elsewhere, or they will starve for lack of proper food."

Many ducks have already adapted

Carr said in waterways like Burton's Pond, ducks have adapted and no longer have any fear of people.

"They've modified their behaviours, because they expect humans to feed them. They're wild ducks, some of them are long-term residents, it's completely atypical duck behaviour. It's a very artificial situation," he said.

Carr said rather than bringing bread, he suggests wild birdseed.

"You can get that at a number of places in town. Also if you go to a farm supply store, they have duck chow, duck pellets, if you want to keep some of that in the car. We usually do that with my twin girls. They enjoy coming down here and scattering some food," he said.

"I have read about it, but haven't tried frozen peas that have been allowed to thaw, because that's soft for their palates. They don't have teeth like we do, so they crush things."

So ... why do ducks cross the road?

Meanwhile, Carr was able to answer a common question: why do ducks choose to cross the road?

He said ducks often choose to walk instead of fly because of the incredible amount of exertion required.

"If a duck wants to get someplace, it's far more energetically efficient just to walk there than it is to swim across," he said.

"If you look at one of the ducks that goes across the pond, there's a large windup ... they're going to soar across the pond and they're going to get to the other side, and that takes a lot of energy. So, why fly when you can walk?"