hello "GROST". i spent a month there in 2010 and three weeks last year, first of all the diving is amazing. in 2011 we i.d.'d 500+ individual giant mantas in three weeks, most days it was literally wall to wall big guys. and they are very interested in us, expect some encounters to last for 10-15 minutes, often they'll even follow you up to your safety stop. it's hard to get out of the water, i've never done so much buddy breathing or so many emergency assents, it just so hard to drag yourself away!!! expect to see many breaching mantas and humpbacks and to hear whales singing while you're under.
bring a warm, water proof jacket to wear on the boat. its an hour or more's boat ride in each direction from puerto lopez to isla de la plata and it can be cool and wet some days and on the way home you'll be tired, so staying warm is key (especially if, like most of us, you want to sleep on the way back). our boats had a head and most people got out of their wetsuits between dives.
the water is cool and some of the thermoclines can be positively cold (mid 60's f). i used a 5mm wet suit with a 3mm shortie over the top and i was cold by the end of the second dive (in the caribbean i dive without a wetsuit). in 2010 some of my group wore dry suits but in 2011 most changed to 5mm, or 7mm semi-dry, except for dr.andrea marshal who just wore a skin most days, brrrrr.
the currents can be absolutely crazy, bring gloves, there will be dives where you will be hanging on for dear life. bring an inflatable sausage and get comfortable with the idea that on some dives your group will get separated and you will be on the surface for a while waiting to be picked up.
also expect to be saddened by the situation, although isla de la plata is supposed to be a protected national park with a 3 mile no fishing zone around it, you will have wahoo fishermen trawling over you on most dives and 90% of the mantas are trailing hook and lines or are horrifically scarred by mono-fiber line. we removed lines from dozens of mantas (it was as if they were coming to use for help, so bring knives but surgical scissors are better) and we air bag lifted hundreds of feet of abandoned nets from the reefs). last year the fishermen had even set up a fuel dump on isla de la plata, less than 500 meters from the park wardens headquarters. add to that the dozens of hammerhead and thresher sharks you'll see laid out on the beach at puerto lopez most mornings. none of the environment laws are being followed and the local authorities are too scared of the ever-increasing number of fishermen to do anything about it. prepare to be depressed.
hopefully you're diving with exploramar dive co., there are a few others in puerto lopez but they seemed like complete cowboys taking really inexperienced divers out to really advanced dive sites, we even saw them dropping tourists onto extreme currents without even a divemaster. dive with exploramar, this is not the place to muck around with amateurs .
if you're looking for an inexpensive but decent hotel in puero lopez i recommend hotel pacifico, its right on the main street right next to the beach. you won't want to hang on the beach much, august-october is mostly cloudy but all the little cocktail stands are fun in the evening.
if i can be of any other help, don't hesitate. prepare to have your socks knocked off, there's nothing quite like a 20 foot giant manta staring very intently into your eyes!