It’s raining, it’s pouring, the divers are snoring

Hong Kong's waters as seen by NASA's MODIS instrument in October 2002
Hong Kong's waters as seen by NASA's MODIS instrument in October 2002
The eastern half is clearly more blue and oceanic, the western half more yellowy from the Pearl River Estuary’s influence
Credit: Jacques Descloitres Aqua MODIS Rapid Response Team NASA GSFC

With the rainy season now in full swing, it’s time to talk colors. Water color that is, and I don’t mean painting, I mean the color of the sea in HK.

It’s actually not the same everywhere, because if you live in Lantau Island on the western side, you are closer to the Pearl River Estuary which carries a lot of mud and silt down into the sea. That makes HK’s western waters murky and muddier, and because the Pearl River also carries a lot of minerals and nutrients down into the Sea, it makes for much better growing conditions for phytoplankton – microscopic algae that float around in the sea. That tends to turn the water color green or yellow, too.
But the eastern side of HK is a different story. Here the water is more oceanic and blue-green because there is no big source of mud and nutrients. Corals love warm, nutrient-poor and sunlit water, so you find them more on the eastern side of HK – basically as far away as they can get from the big rivers.
So what’s all this got to do with the rainy season? Well, a big tropical downpour washes soil, nutrients as well as all sorts of rubbish off the mountains and into the sea…anywhere, so river or no river, the water goes yellowy-green.

If you are a diver, this gives you two rules of thumb for visibility in HK waters:
– East is best, west is worst
– don’t bother diving after rain: the more rain, the longer you have to wait for decent visibility to return. For your typical typhoon I estimate at least 5 days.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s