Firefighter Craig Smith had an audience of hundreds of revellers when he asked girlfriend Danielle Buettner to marry him.
The 24-year-old decided to pop the question before the start of the Geddington Squirt charity event on Boxing Day.
He climbed a ladder to reach Danielle, 25, who was standing on the bridge at the River Ise ford, waiting to watch the traditional fundraiser.
Craig then popped the question and presented his girlfriend of eight years with a diamond engagement ring.
When Danielle said yes a cheer went up from the delighted crowd.
The couple, of Station Road, Kettering, will now be thinking about setting a date for their big day.
Nursery worker Danielle said: “I said yes and then I cried. I had no idea what Craig was doing when he started to climb the ladder.
“I thought it was something to do with the event. I was completely surprised.
“It was wonderful. We have talked about getting married but mostly it’s been in a jokey way.”
Kettering firefighter Craig had been planning the proposal for two months.
He said: “The people I work with knew what I was going to do and some family members were in on the secret.
“I was a bit nervous but really happy when Danielle said yes.”
Spectators congratulated the happy couple and the county’s chief fire officer, Martyn Emberson, who was also at the event, said: “It was a very special proposal.”