People who want to go fishing in small boats this summer are being advised not to get impatient if the weather's against them because of El Nino.
Niwa says the current El Nino pattern will continue for at least the next three months.
El Nino can lead to intense storms in some places and droughts in others, and the current one is one of the strongest on record.
Recreational Fishing Council vice-president Sheryl Hart said it was generating more frequent rough seas and big swells that often prevented smaller boats from going out.
She said people needed to be careful.
"Fishermen who are probably starting to get desperate because they want to go - your life it's worth a little bit more than that.
"The dance of the desperate shouldn't be held with bad weather forecasts and horrific sea conditions, just tie ho - it's not worth it."
Mrs Hart said during three weeks on holiday she could only go fishing three times because of big swells, which was very unusual for this time of year.
President of the council, and head of Our Fishing Future Geoff Rowling said another concern was people who were fishing from land.
Mr Rowling said the majority of people who drown while fishing on rocks were immigrants who were not used to New Zealand's coastal condition and large swells.
He said the unsettled weather could make the west coast in particular a bit risky.
"We're getting an increased number in drownings, so that's something for people to look out for, particularly in this weather pattern that we seem to be in at the moment, a lot of westerly swells are coming in and there's a few of them that are bigger than others.
"People need to be careful when they're shore based fishing that they don't get swept off the rocks."