Historically, it’s been first come, first served.
Colee Hammock Park is a city park on the waterfront around the corner/down the street from the Episcopal church (across from the main entrance to First Presbyterian Church). Again, historically first come, first served. No tickets available or required. There’s ample parking, but please observe signage.
if you’re staying on the south side of the river, Smokers Park is an equivalent view, and much easier to get to from SE 17th Street. I grew up living on SE 11th Street and went to First Presbyterian Church through high school, so am pretty familiar with the area.