This happened to me just this last weekend while on a live-a-board in the Channel Islands. I am new to diving with only 31 life time dives. All cold water. At any rate, we were aboard a 70 foot dive vessel with it's diver down flag flying. A while earlier we had noticed a smaller boat coming pretty close to us with divers in the water, then it would take off for a bit and suddenly reappear. It was a boat run by a popular divers supply off of one of the islands. As we were getting ready to suit up for one more dive, our skipper suddenly called a pause and asked for us to wait until all of our divers came aboard. Once a head count was taken he informed us that we were not to get back in the water until this smaller vessel had dropped it's anchor. We waited, got a bite to eat and suited up. They dropped anchor and we watched their divers enter the water. For us, it was the last dive of the trip and myself and my buddy were released by the captain to go back in. As we were looking for our anchor line to start our ascent, we inadvertently overshot it and paused to look for some natural nav spots to help us figure out where we needed to head. I looked down at my compass and suddenly heard a very loud sound above us. We were in relatively shallow waters at this point and it didn't sound like our boat or our boats compressors so we started to descend a bit. Then another noise that was much louder caused us to both stop which in retrospect may not have been a good idea, or may have saved my buddies life. Just as we stopped to determine the sound again, I saw a large boulder/rock flip up and an anchor suddenly pop up and drag its self right next to my buddy, over the reef and up to the surface as an engine screamed. Well... we quickly realized where we were under water and back tracked to our own boat. As we back tracked, we found a group of four divers just seconds from where the anchor was ripped up and their tanks were all marked by the same company. I thought maybe they had been left by their boat. we attempted to get their attention but they seemed like they were on a tour of sorts and had no worries. I was running very low on air and we still had to find the anchor line. We eventually did and once back on the boat we told our crew what had happened and they indicated that AFTER they had their divers in the water and AFTER our captain told them we were in the water, they decided to throw out their stern anchor because apparently they only had a bow anchor set before. That must have been the first loud noise we heard. Our crew said also that they didn't receive any radio communication that they were going to start their engines, maneuver in the water or pull up the anchor after they threw it. So this boat, maneuvered in the water, tossed and pulled up an anchor knowing that there were at least four of it's own divers in the water and two more from another boat. What is even scarier to note is that there WAS a diver down buoy on the water as well. The only thing that we could think of doing when we heard the unfamiliar noises was to get deeper. Not sure if that was the right thing to do but at the start of our trip I remember our captain giving us a long briefing that had a five minute section on a procedure for an emergency maneuvering of the boat while divers where in the water. It involved a recall siren and all divers surfacing for a head count. This smaller vessel didn't seem to do any of that. Just plopped an anchor in and pulled it up with out care to any of the divers. Even their own.
