Oil leak.

I have a 1994 Sunbird with a 4.3 liter corba engine. I runs great but when I shut it off out in the middle of the lake there is a oil slick behind my boat. I am not much of a mechanic but would like to know what is leaking before I take it to a mechanic. I do know it is motor oil because my engine runs low of oil at the end of the day. Also I know the block is not crack because the oil in the crank case is clean. Would appreciate any help. Also getting a small amount of water in the bilge. Please email me a [email protected] with suggestion.
Thanks

Welcome.
You shouldn't include your e-mail in the post.
What's the model#,serial#.Always include when asking any questions.
Fill out the profile,location. You might be close to someone who can help?
If they need to send you any info it can be sent in a post or a private message.
AS far as the oil leak, you have an oil cooler in the system?