The brave Long Island boy who watched his father vanish under the water after a kayaking accident bid him a final farewell yesterday at a packed funeral in Smithtown.

More than 200 people — many of them uniformed officers — gathered at St. Patrick’s Roman Catholic Church to mourn the loss of NYPD cop Patrick Luca.

The police recruiter drowned in the Nissequogue River on Sunday after setting out in an inflatable craft with his son, Caden, 5.

Officers knelt down to comfort the youngster as he passed.

The boy was miraculously rescued by passing boaters who found him floating in a life jacket.

Luca’s wife, Stephanie, sobbed inconsolably as she followed the flag-draped coffin from the church.

Cops have been unable to pinpoint the cause of the accident Sunday afternoon and are still investigating Luca’s death.