Two years since the Rena grounded, Tauranga beaches appear to have recovered with no recent signs of tar spots.

But what's brewing below the surface and the long-term effects of the grounding are subjects of research and monitoring, and next month a series of scientific environmental impact reports are expected to be made public.

Speaking from Wisconsin, University of Waikato Professor Chris Battershill said a range of impact research projects had been conducted during the past 20 months.

The Tauranga-based professor said once peer reviewed, the reports would be released to the Environment Ministry, Bay of Plenty Regional Council, and other key stakeholders, including iwi, before being released to the public.

Research showed local beaches and most of the off-shore islands from Waihi to the Bay of Plenty's east cape had recovered "extremely well" because of the massive clean-up efforts .

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.

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No sign of 'Rena' oil on BOP beaches