mrdylan,
In response to your questions.
The fish you are seeing in Oshawa creek during the early spring are steelhead trout. During late spring / early summer you can catch some real nice smallmouth bass and the odd northern pike. During the fall you can witness a terrific salmon run. I personally don't eat fish from that creek but people do.
Enjoy the Oshawa creek, it really is a great fishery in your own backyard. Please practice sound conservation and like the others said; its best to get out and discover it for yourself.
Looking forward to the spring!