During the construction phase of the Bluff Branch, contractors found that landing urgent supplies at the Invercargill wharf could prove difficult due to the worsening danger of the New River estuary silting up dangerous sand bars. Contractors were having a difficult time building over and around the upper reaches of the estuary and getting equipment into the area proved troublesome. At the mouth of the estuary was the moderately deep and weather sheltered entry to the Mokomoko inlet. A Jetty already existed at the eastern side of the inlet entrance for the local settlers and at one point was promoted as an alternative to both Campbelltown and Invercargill's port ambitions. It was decided to lay a spur line off the still incomplete Bluff mainline to the jetty which consisted of a large curve that required deep drains on each side. The junction points faced Awarua with a small flag station controlling the points.