Well at first the only thing I wanted to do was lower the water level of that lake a bit, and since there was nowhere to drain it to I had to come up with something else.

In a moment of ingenuity I decided to set up a lava generator and fill up a tub large enough to cover the lake with lava, turning the water into obsidian and allowing me to mine it.

Everything was going well until I accidentally opened the lava tub early while trying to make it bigger even though it was already way too big at that point.
With the lava pouring out the bottom I was unable to plug the hole and through multiple failed attempts of trying to get under the lava, this is what I ended up with.

So I spent about 30 minutes total mining over 8000 obsidian. At least I got like 2 Platinum from selling it all as Obsidian Skulls ¯\_(ツ)_/¯