Picton Ecoworld Aquarium manager Regan Russell said four penguins were brought into the aquarium last week.
One penguin appeared to have been hit by a boat and suffered extensive internal bleeding, while another was found on Queen Charlotte Dr near Momorangi Bay with injuries to its head and leg. Interislander ferry staff also found a baby penguin weighing less than 400 grams. All three died within hours of arriving at Ecoworld, Mr Russell said.
One penguin, named Flipper by Ecoworld staff, appeared to have been mauled by a dog and had one of her flippers bitten off, but was was making a good recovery.
Many penguins are found onshore in the Picton area during breeding season, which ended last month. Mr Russell said some penguins might have hatched a second lot of eggs and still be onshore.
"The problem with penguins is they nest under baches and the yacht club, which is close to the dog track.
"They like to nest close to people. Why have a burrow when you could have a bach?"
Penguins also came ashore to malt their coat after breeding and had to stay on land for about a week until their new coat was waterproof.
Ecoworld has received about 20 penguins, but this is the first time any have died.
"It's very unusual. We've been doing this [working with penguins] for only two years, so it might be that more people know about us and are bringing them in," he said.
Department of Conservation biodiversity assets manager Mike Aviss said people in Marlborough Sounds should be aware of the wildlife around them.
"It's a bad time of year [for penguins], with a lot more people here. It's a broad issue, which gets bigger as the population grows," he said.
He said boats, pets and traffic all impacted on penguins.
"We're lucky we have safe breeding areas on our islands, as without them, the penguins would struggle more than they are.
"People just need to be aware of the place they're in.
"People are conscious of their impact on fishing stocks, but they probably don't think of the other impacts of them just being here."
- The Marlborough Express