Excessive White smoke and oil pressure drop 2007 Tige wakeboard boat

I have a 2007 Tige wakeboard boat with a GM 350 engine. This weekend as we were driving up river I noticed the oil pressure gauge drop instantly and my boat start to lose power. I turned off the engine just as the oil warning sound came on and put the throttle to neutral. I noticed smoke coming from under the cover of the engine and when I removed the oil dipstick, some smoke was coming out of there as well. I let the boat sit for an hour and started it again. I noticed excessive white smoke coming from the exhaust under the water but the oil gauge and temperature gauge were reading fine. I throttled up to 2000 RPM then 3000 RPM when I noticed the oil gauge dip again and just as my boat was about to die I turned it the engine off. There was no smoke coming from the engine compartment only the exhaust. I was able to drive it back to the docks at 2000 RPM with no faultering of the oil gauge or temperature gauge but A LOT of smoke coming from the exhaust. people thought my boat was on fire. I looked into the engine compartment and again no smoke, only from the exhaust.......Any ideas on what this could be???? Scott

was it the first run of the year or have you been using it before this summer? is it fresh water cooled? the blocking plate in your riser may have deteriorated. you should post this message in the engine specific forum, you'll get more help there.