Some of Adelaide's metropolitan beaches have become smelly & slimy spots to snorkel & scuba dive. The source of the smelly slime is said to be rotting carpets of posidonia seagrass seeds floating ashore. It is a seasonal event brought on by hot weather. This is also the season for the proliferation of Giffordia, a slimy alga which adds to the smelly odour on our beaches. The alga also causes low visibility in the water where it occurrs. 10 or 11 years ago, I was told that the outbreak of it was caused by sewage/sewerage effluent entering the sea. A government marine biologist said at the time that it was non-toxic and harmless to humans. She said that it was usually found attached to rocks offshore, but that it grew quickly in certain warm weather conditions, broke free and drifted ashore. I have posted a marine life beachcombing guide in Windows Live. See the link to the Guide in "My Links" on this blog. The 3.5mb Guide can be downloaded from Live.