About 20 hardy souls took the plunge at Tikitapu (Blue Lake) as the NZ Bomb Comp kicked off on Saturday.
Despite the rain, a small crowd was starting to build from 10am as people leapt from the Bomb Tower, hoping to make the biggest splash.
As he dashed out of the lake and back to the tower for another jump, Selwyn Robson gave the event a thumbs up.
"It's good eh."
While it was raining, it was warm in the lake itself, he said.
Another bomber described the event as "cool as".
For those not willing to get in the water, the music was pumping and there were plenty of food stalls to browse.
While Saturday was just for fun, the real competition would take place on Sunday.
Casual bombing costs $8 to $10 for five jumps and day passes are also available. The platform is multiple levels, up to 10m high.
The largest prize in the competition is $2000 for the open male division. Another $3000 cash and other prizes are available across the seven divisions.
On Sunday, finals are from 3pm to 5pm.
Bombing will be open from 10am to 6pm daily and 11am to 4pm on Waitangi Day.
The hīkoi is expected to arrive at Parliament around midday.