Jonathan, If your staying in Needles, your best bet might be to board there early in the morning. The water is sweet there in the mornings, but it's a lot cooler than havasu so you might wanna bring a wetsuit along for your first runs. Then head down to the sandbar, to watch the animals play.
Skiers Cove that Luke mentioned is nice in the mornings also till around 10am, but it's about 1 hour by boat from needles. So getting up at the buttcrack of dawn is required.
Have Fun. I wish I was going