nevermind, just found this again in my manual. my guess is your seacock was open.
N O T I C E
If the livewell seacock is left open and the pump is not on, the boats forward motion through the water will gradually fill the box. To prevent this inadvertent filling, close the seacock when the livewell is not in use.
N O T I C E
Under certain conditions, placing the outboard engine(s) in reverse will ventilate the water under the boat and create an air lock in the livewell pump. To prevent this situation from occurring, it is recommended the livewell be turned off prior to any high RPM or continuous reverse operation. If the livewell pump becomes air-locked, correct this situation by turning the pump off for 20 seconds.