As other have suggested the Aquatic Center on Kimball Rd (Ventura Community Park) is a beautiful facility for swimming. You can even pair a run with your swim by running on park property and there is a bike path that goes out the back end of the park and you can do a nice out and back without risking losing your bearings in an unfamiliar place. Other than Kimball, if you are a YMCA member or are interested in a guest pass...there is a pool at the Ventura Family YMCA on Telegraph Rd. (Ventura). Lane availability is a bit more suspect due to swim lessons etc, but an option nonetheless.
As for cycling...it all depends on what you'd like to do, there are some great loops/routes that include the coast and hills...From Oxnard you could head into Ventura via Harbor Blvd and then wind through Pierpont/Ventura Keys, the Ventura Promenade and then up the bike path, along the Rincon (RT1) and continue riding along the ocean up to Bates Rd. From there, the choice is your (head back, head inland up some climbs or continue north).
Lastly, there are at least two run races happening on the 4th of July - The Ventura Promenade 5k and there is the Fourth of July 5k in the Channel Islands.
Feel free to drop us a line at Hypercat Cycleworks / Hypercat Racing for further info...we'd be happy to help.
:) Rachel
Rachel Sears Casanta
www.hypercat.com 805-477-0353
rachel@hypercat.com