Guest post by Nina Khashchina My first experience with sketching while scuba diving was in 2012 in Roatan, Honduras. Here I am, sketching underwater! 
I cut in half a Rite in the Rain Polydura 8.5" x 11" sketchbook. Other equipment: a pocket on my belt, a regular #2 pencil, and a 4B carpenter's pencil. 
On the first trip I sketched on six dives and learned a lot: 
All in all, sketching underwater is A LOT OF FUN. Try it out, have a blast, and tell me about it! Nina Khashchina lives in Palo Alto, California and blogs her sketches here.
• Drawing required better buoyancy control and awareness of environment. I got better, but need more practice. • Spare pencils are handy. I broke one - not sure how. Seawater and depth make pencils fall apart quickly, not to mention runaway pencil ascents and pencils swimming away during boat boardings. • I attached a string to my pencil - it's still underwater somewhere, even though the pencil surfaced with me. • You can get really close to some subjects and they will stay still! Be careful - some might sting! • Many subjects are like kids - moving all the time. • Some pages were built gradually, adding bits and pieces to one page from different parts of the reef. • Carpenter's pencil was good for drawing motion - but too fat for details or notes.
After each dive I would tear pages from my sketchbook, rinse them in fresh water, and lay them out to dry. Later I taped them in my main sketchbook and added additional notes. 
My second experience with scuba diving and sketching was in 2013. I spent seven days at sea diving from the boat on a trip from Saba to St Kitts in the Northeastern Caribbean. This time I had COLOR! I used the same sketchbooks and #2 pencil, but I added a red-and-blue pencil. The softer lead was the most useful feature. No matter how soft the regular graphite pencil, it still feels very hard at depth. 
My second experience with scuba diving and sketching was in 2013. I spent seven days at sea diving from the boat on a trip from Saba to St Kitts in the Northeastern Caribbean. This time I had COLOR! I used the same sketchbooks and #2 pencil, but I added a red-and-blue pencil. The softer lead was the most useful feature. No matter how soft the regular graphite pencil, it still feels very hard at depth. 
This spring I spent a week drawing underwater off the Caribbean island of Bonaire.
I had a plastic, mechanical Aqua Pencil with me. Its thick lead and no metal parts made it a winner. It is as good as new after a week in saltwater! Another important thing is that the lead advances when you twist the back end of the pencil - and not push it. I threaded a piece of elastic band through the handle of the pencil and kept the other end on my wrist all the time - this helped a lot with the "I'm going to lose my pencil or will not have enough hands or attention to be safe under water" anxiety.
The highlight of the trip was seeing a porcupine fish do its signature trick of inflating its body by swallowing water, thereby becoming round. We were a bit far away from this event as it happened but I was able to sketch it as it takes a little while for the fish to go back to normal. 
