A group of Dive Otago students and instructors visited the Blue Lake at St Bathans in Central Otago earlier this month to help clean it up and for students to learn how to dive against debris.
Dive Otago general manager Virginia Watson said the Blue Lake was chosen as they had not done a cleanup there for a while.
A man-made water body, the lake is the result of sluicing operations that began in 1873 — turning a 120m-high hill into a 68m hole.
It was abandoned in 1932 and natural drainage from the surrounding hills filled the hole to create the Blue Lake.
Before the debris dive took place, the lake was more green than blue.
Over the day the eight students collected 7.5kg of rubbish.
One of the more interesting finds was a turbine roof vent, commonly known as a whirlybird, Ms Watson said.
It was unclear how it ended up at the bottom of the lake, a popular recreation spot.
A chimney top or toilet top was stuck in mud at the very bottom and try as they might, the divers could not lift it from the lake bed.
"There was just lots of recreational gear, like fishing rods and stand-up paddleboards, things like that.
"None of it looked like dumping. It’s all kind of accidental stuff.
"Also found a few beer bottles and things like that.
"Chip packets and pie wrappers."
She said it was disappointing to see rubbish in the lake.
"A lot of stuff does end up in the water through sort of accidents.
"So, you know, no-one wants to drop their fishing rod or their stand-up paddleboard.
"Obviously, it’s always disappointing to see the beer bottles and any kind of food packaging."
They brought all the rubbish back to Dunedin to categorise and record it systematically.
The dive school’s students found it rewarding doing something new and learning new skills, Ms Watson said.
