I did some golf ball diving myself back in my high school days - but nothing as advanced as what we see in the video. No wetsuits, no snorkel. Just a scrawny kid in jean shorts going into the water.
Our tactic was to stick to the shallow waters and use our feet to feel the balls. That meant walking barefoot through the muck. Which also meant choosing our ponds carefully. Snapping turtles? No thanks, I like my toes.
The golf course we worked used effluent water in all its ponds. Which is pretty disgusting thinking back on it. At the time it didn't bother us. We'd fill up a pillow case with balls, then walk the course offering 10 balls for a dollar to each group of golfers we ran across.