Check out the summary by Heidi Sosik of Morel et al.'s "Optical properties
of the 'clearest' natural waters" on p. 21 of the latest L&O Bulletin.
http://www.aslo.org/bulletin/issues/07_v16_i1.pdf
Stealing a bit of thunder from Heidi's summary, Morel et al. find natural
water in the S. Pacific gyre that has lower UV absoprtion than Smith and
Baker (1981) "clearest" water. Very cool.
Note that this Morel et al. L&O article was selected by ASLO for free
download:
http://www.aslo.org/lo/pdf/vol_52/issue_1/0217.pdf
/eric rehm