A Far North Queensland community is mourning the loss of a large saltwater crocodile believed to have been deliberately shot.

Bismarck, estimated to be up to 100 years old, has long been a part of the small seaside community of Cardwell, south of Cairns, and was often seen cruising along the foreshore.

The body of the 4.5-metre "gentle giant" was found with bullet wounds, in a creek, near a boat ramp.

Now, residents are planning a "memorial day" for the big saltie.

"It's very, very sad for Cardwell," long-time resident Thea Ormonde said.

A gentle soul

"We saw Bismarck as part of our community, he was such a gentle soul as far as crocodiles can go," Ms Ormonde said.

Bismarck the crocodile was often seen cruising along the foreshore of Cardwell in far north Queensland. ( Instagram: Soobeedee )

"He was one of us."

She said as a child, she would go crabbing with her father and they would often watch him, sunning himself on the bank.

"He was never aggressive, he would always let people know he was around, he was never stealth-like or would attack people," Ms Ormonde said.

"Bismarck was protecting us because we always knew where he was and he kept other male crocodiles at bay.

"It's going to be quite dangerous now because there's going to be a fighting war to claim the territory."

Another resident, Ryan Moody, filmed the dead crocodile and posted it to social media.

"This croc was never a threat to humans, he just loved a feed of turtles," Mr Moody said.

"I used to walk right next to him at the mouth of Meunga Creek while gathering bait and flicking lures.

"Let's just hope the big aggressive crocodile from across the channel doesn't move in.

"It's amazing how humans can make situations become more dangerous through acts of pure stupidity."

Police are investigating the cause of the death and Queensland's Department of Environment and Science is also looking into the matter.

Public service planned

Ms Ormonde said the community was planning a memorial for the big boy.

"I would really like to organise a memory day or a goodbye-to-Bismarck day that I would like all the community to come along to," she said.

"We want to remember the gentle giant because he never caused any problems for anyone."