There will be a lot of people on Saturday. I'm sure a few will be, but most will not be early birds after likely "socializing" to a late hour on Friday evening.
I'd guess very few will push off for their initial outing that day before 9 a.m. Many will be closer to lunchtime. And those that do leave early may return in the afternoon before setting off again for a separate evening trip.
In other words, there will be a lot of people there in the morning and there's likely to be at least a few around at any time of the day. Most of them will have made groups and plans on Friday night, but most will also be happy to include a last minute addition to their party. Since you'll be arriving after the plans have been made, just don't be shy. Approach people and start conversations, let them know you're looking for someone to fish with. And have your stuff reasonably ready to go so if anyone says "you're welcome to join but we're leaving in 5 minutes", you can grab your stuff and go.