The Tairua River starts deep within the south end of the Coromandel Range, runs through the historic gold mining area of Broken Hills, then through Hikuai out to Tairua Harbour. From State Highway 25, Puketui Valley Road more or less follows the river to the walking tracks and DOC campsite at Broken Hills.
There are several places to access swimming holes along the river before Broken Hills. They are unmarked, so it may take some trial and error or local advice. Another option is to put a kayak into the river at the campsite, then float and paddle down to Hikuai through a mix of native forest and farmland. Take a stop or two at the swimming holes. At Hikuai, go under the State Highway 25 bridge and look for a small but steep sandy/grassy egress area on the right.
It is mostly sedate with some shallow, gentle, low-grade rapids. Avoiding getting stuck on the bottom of the rapids is more challenging than getting through them! It may even be too shallow after a dry spell.
The trip takes a couple of hours. It is not the most adventurous kayak trip, but it is safe and suitable for beginners.