"I spent a lot of my summers when I was growing up with my Dad who lived in Sydney, on North Sydney beaches ... and always felt comfortable in big waves but I've got to say that ... really, it's just too easy to die, to put it simply.
"And I think everybody's default is that you think you're going to be ok but it just shows that it can happen so quickly."
On Saturday, he took Henrique with partner Carla Amaral and and his two sons to Pakiri Beach after finding Goat Island too rough.
Birss and Henrique went for a swim, while Amaral looked after the two boys.
Noticing conditions were worsening, Birss yelled out to Henrique head back in.
"It was like a washing machine out there. I saw a girl on a board and she was kind of bobbing around ...she was young. I didn't have very far to go to her, about six to eight metres. I went over and grabbed her and said 'it's ok, you'll be alright'.
"I was up to my neck but could get my footing and quite fortuitously a nice forming wave came and I pushed her and she got it."
Then he saw two men about 10m away.
He swam towards the man who had his hand up but then lost him.
"It was really windy, you could see each other for a minute and then you couldn't because of all the waves ... but I couldn't find him, I didn't know where he was, I just lost sight of him."
The man re-emerged and Birss got to him.
Now shoulder-deep, Birss struggled with footing as he got pounded by waves.
"I just held the back of the guy's head and got semi-under him and held with one hand his head up and my other hand I was walking backwards as quickly as I could."
Henrique then swam over and helped drag him to shore.
"I had him and then the waves would wash over us, and I'm trying to keep his head above water ... we got to about thigh deep and we were yelling and trying to keep moving because we wanted to get him to the beach to get some breath in him pretty quick and then three ladies came out, and we dragged him clear of the surf."
Birss along with a couple of others carried out CPR for the next 30 minutes until emergency services arrived.
The second man who had been struggling made his own way to shore and was helped by beachgoers.
"You're really willing someone to do the big cough and it never came and there was a group of us who tried really hard to make it happen and it was just an avoidable tragedy."
Jonty Mills, chief executive of Water Safety New Zealand, said while he couldn't comment on the drownings specifically, it was a good time to remind people to swim within their limits and if in doubt, stay out.
The men's deaths put the drowning toll at 20, compared to 24 at the same time last year.