The Yakima Delta is formed as the Yakima River empties into the Columbia River. There is an amazing amount of wildlife from fish, birds (pelicans, hawks, the occasional bald eagle, and owls), deer, and river otter.
All were paced via kayak and unless water levels are low should be access able without having to exit your boat. The water level fluctuates here quite a bit and you will find it very shallow or in mud flats to a point where it's so high you can paddle right over the islands. Check here for the latest official water level: http://waterdata.usgs.gov/wa/nwis/uv?site_no=12514500. The level was a bit higher then normal the day I placed this cache with the gauge reading 339.5 feet. There is very little water current in most areas but if windy he water can become choppy with even a gentle breeze. Motor boats will be hard if not impossible to maneuver in most locations.
Enjoy the scenery, grab any trash you may encounter and happy caching!