Police had released the name of a man who went missing while swimming in the Whanganui River at the weekend.
He was Duane Kaka, 34, of Wanganui.
A police dive squad from Wellington joined a search today but the fast-flowing, murky water from recent downpours had not provided ideal conditions, police said.
Searches would continue by boat over the next few days and with fine weather predicted the river conditions were expected to improve.
Ruapehu police Area Commander Inspector Steve Mastrovich said police held grave fears for Mr Kaka's safety.
He acknowledged the assistance given to the search so far by the Department of Conservation, search volunteers and the commercial operators of jet boats on the Whanganui River.