Although that was great news, he said some areas were still subject to intensive monitoring, including Astrolabe Reef and around the wreck.
Prof Battershill is leading an Environment Ministry-funded study into eco-toxicity, including research on the mixture of Corexit and oil in this country's sea temperatures.
The study was due to take at least 18 months, he said.
Corexit dispersants were used during the clean-up and sprayed on deep water about 20km off the coast of Tauranga in days following the October 2011 grounding.
Prof Battershill is in Wisconsin for a week-long World Environmental Restoration Symposium.
He is one of the keynote speakers talking about environmental recovery from pollutants in oceans and seas, including sharing his research into the Rena oil spill.
Rena Recovery Programme manager Warwick Murray said although tar spots were occasionally being exposed after a storm, it had been weeks since there had been the need for a major clean-up.
Hundreds of people hit the Mount Main Beach and Papamoa Beach yesterday, and there were no signs of oil or the troublesome beads which earlier washed ashore.
Papamoa Beach resident Kathleen Andreae said that three weeks ago she had to snip off bits of tar from her pet's fur, but the beach had been clear of oil and little beads since.
"I hope this means we're finally seeing the last of it [oil].
"It's taken a long time to recover and I hope it's a sign we're going to have an oil-free, fabulous summer."