I recently started surfing and really like it! 
I've always wanted to try myself.  When I was younger, there was this lake that was surprisingly suitable for surfing nearby.
What made it suitable for surfing? 
I guess you can say that the waves were artificial, being created by the water falling out from this hydroelectric damn that fed this lake.
I haven't heard of artificial waves, are they different than regularly occurring waves? 
Maybe.  These were caused by the displacement of water from the turbines in the dam, so if it was turned off for whatever reason, there were no waves.
Do they turn it off often? I would hate to be out there and no waves on my day off.
Not often, and when they do, people just go wind surfing or body boarding.  There's always another form of surfing to do there.