From Tua Marina there was once an almost impenetrable swamp until the valley floor rose to higher ground at Para where there was heavy bush through Koromiko to Mount Pleasant, then a rise over the Elevation, still thickly wooded, then down to the Maori Pa of Waitohi, named after Te Rauparaha's sister. It is generally believed that Tua Marina means 'the Calm Beyond'. Could this refer to the relief of a traveller to Tua Marina after traversing the tangle of rough vegetation and uneven ground of the Swamp?

In December 1842 Frederick Tuckett, chief surveyor of the New Zealand Company, exploring up the Tua Marina stream, attempted to penetrate the swamp. At the best he considered he made progress of one mile per hour and gave up as he could afford no more time. Later, after the survey of the Tua Marina area was completed on 29 May 1843, Surveyor J. W. Barnicoat with two of his men climbed to the top of Strachan's Peak looking for a route through to Waitohi. From there they could not see the Sound and returned baffled to their camp at the foot of Massacre Hill. Had they climbed Dobson on the other side of the river the waters of the Sound would have been visible.

It was left for Company Surveyor Samuel Stephens with William Fox, Renwick, Jollie and Wells to find the way through. They arrived at Waitohi Pa on 5 March 1845 by boat. They were surprised to find a wide well-beaten track over the Elevation, this was used for dragging out totara logs for canoes. There were also extensive gardens particularly on the Waitohi side of the hill. It has been suggested that canoes were portaged to the Wairau river through the Swamp. As it had been a very dry summer the swamp would have been easier than usual. They did not retrace their steps but returned to Nelson via Tophouse. Four months later, in July, Dillon Bell led a party through. Both Fox and Dillon painted water colours of the plains from above Tua Marina, these are still in existence. No doubt other parties negotiated this route and Picton was surveyed in 1848 but there is record of only one pakeha family, McDonalds, living there.