A section of the old Salisbury and Southampton Canal passes Holy Trinity. The only extant original bridge of the canal is located here. It consists of a single arch built in brick, and it is a Grade II listed structure.

In 1789 an Act was obtained for the Andover and Redbridge Canal which followed the course of the Rivers Test and Anton to Andover. In May 1795 the Salisbury and Southampton Canal received royal assent for its bill to construct two branches to the Andover Canal: one following the River Dun from Kimbridge towards Salisbury, the other from Redbridge along the foreshore to Southampton. Work commenced in August of that year. The construction of the canal proved more than difficult, with sinking sand creating great problems. The original estimate of £784 per mile for the canal between Lockerley and West Grimstead prove to be a gross miscalculation and the eventual cost was over £2000 a mile.

The canal was completed beyond West Grimstead into Alderbury and Tunnel Hill by 1806. As the costs escalated, it became clear that the canal was unlikely to give any return on any further investment and no more loans were forthcoming.

By 1808 traffic that had been using the canal on the Redbridge to Southampton line ceased and soon after that, it ceased on the Kimbridge to Alderbury line. Without maintenance the canal fell into ruin.