A man has drowned after jumping into the river at Port Adelaide in an attempt to save his dog.

Witnesses said they saw the incident happen at about 11:30am today.

Emergency services managed to pull the 53-year-old local man out of the water after he struggled to make it back to shore, but paramedics were unable to resuscitate him.

No-one else was injured.

Witness John Bunny said another man spotted him struggling to reach the ladder, but was unable to reach him quickly because a nearby premises was locked.

He said once that man finally made it down to the wharf, he "stripped off" and jumped in.

But Mr Bunny said the man was already lying face down in the water and was unconscious.

"If he had been stronger, maybe he could have swum back to the ladder — he was not far away but he couldn't make it any further," he said.

Mr Bunny said emergency services pulled the man from the water and started CPR.

Police said there were no suspicious circumstances and officers would prepare a report for the State Coroner.

The dog survived.