The imaging resource review hints at this problem, though they only test in a pool.
These lenstip underwater reviews are great. They test and comment on all aspects, of underwater photos and video, at snorkel depth, and a deeper.
They haven't covered the tg-1 yet, but tg-820 had similar issues!
Based on this review, the canon d20 is operable down to 30 meters! And works great IQ and WB wise, at greater depths, but has issues of too much contrast, at snorkel depth.
And panasonic TS4, (FT4), only works to the rated depth +1m, but works better, IQ wise, at the snorkeling depths.
I have both on the way, and will report back. And send back, the looser.
Edited by derway, 17 November 2012 - 11:58 AM.