He pulled over near the Waitangi roundabout and realised there were three orca just beyond the surf line, only 5-10 metres from shore. He dropped his customers off at Waitangi Bridge so they could walk along the shore following the orca as they first checked out the jetty at Waitangi then doubled back and cruised slowly south along Ti Beach, chasing stingrays as they went.
A woman was swimming about 10m from the orca, unaware she didn't have the water to herself. The divers told her she had company and she promptly exited the water. Mr Johnston said she was not in danger.
"They were busy chasing stingrays. She didn't look like a stingray," he said. There have been no reported cases of orca attacking humans in the wild.
The divers followed the orca for at least 15 minutes before they disappeared around the Bluff.
The visitors hopped back in the van and caught up with the pod at Paihia Wharf, where eagle rays were leaping from the water trying to escape. The last they saw of the orca was as they were heading towards Opua.
Mr Johnston said his customers were "blown away".
"They're all water people, all divers, but to get that at the end of the day was a real bonus."
Among those on the dive trip was Dutch-born Sea Shepherd skipper Wyanda Lublink, who had been enjoying some leave in New Zealand.
A few days earlier she had been diving at the Poor Knights where she had seen sunfish and sharks. She told Mr Johnston the one thing she still wanted to see was an orca.
Mr Johnston joked, "I'll book them in for 2pm". They were two hours late but no one was complaining.
Only a few hours earlier, on the west coast, a pod of Orca delighted a crowd of about 80 police officers gathered on Ninety Mile Beach for their annual surfing contest. The officers, representing every district in New Zealand, were competing in the 12th NZ Police Association Board Riding Champs which kicked off on Monday.
But conditions on Tuesday meant the heats were temporarily halted in surf near Waipapakauri, about 10km north of Kaitaia. Officers had been checking conditions further down the beach and were on their way back from Shipwreck Bay when they spotted the pod of five orca heading north in the surf.
Surf life guards helping with the surf competition followed the pod as they surfed the waves when a large male in the pod gave them some closer attention. The bull approached the inflatable boat and gave it a bump before the lifeguards decided to head back to shore and leave the pod to continue their northward journey. Most of the officers viewed the spectacle from the safety of the dunes.
