The number of hector's dolphins dying increased by two thirds in 2007 and more needs to be done to protect them, Forest and Bird says.
Department of Conservation figures showed 25 hector's dolphins, which are an endangered species, were found dead in 2007, up from 15 in 2006.
Forest and Bird conservation advocate Kirstie Knowles said the Government needed to act.
"Interim measures requiring that people don't leave set nets unattended in Kaikoura and Te Waewae Bay in Southland are not stopping dolphins from being killed.
"Comprehensive protection is urgently required if we are to prevent further deaths."
It was difficult to determine how the dolphins died because of decomposition, but one was confirmed to have been killed by becoming entangled in a set net.
A net was "probably" the cause of another death and "possibly" the cause of two others, Ms Knowles said.
Three were confirmed to have died of natural causes.
"The official figures are just the tip of the iceberg. We need to get serious about protecting them from human-induced threats.
"A comprehensive threat management plan including a total ban on set nets is urgently needed to protect this endangered species."
Ms Knowles said the Government had planned to implement a plan outlining protection measures for the dolphins by the end of 2006, but it had been delayed until March this year.
The interim measures put in place while the plan was being developed had done little to prevent deaths, she said.
The Government's condemnation of Japanese whaling was hypocritical when the dolphins, which were more seriously endangered, were not adequately protected in New Zealand waters, Ms Knowles said.
"We can't be taken seriously in criticising another country's actions in threatening endangered marine mammals while we are allowing our own endangered marine mammals to be killed at home."
The hector's dolphin is the world's rarest dolphin. About 7000 remain, down from about 26,000 in the 1970s, when set nets began to be widely used.
Set nets are banned or heavily restricted in many countries worldwide, including Australia, the UK and USA.
