Riet itself has very little to offer... Possibly some sports to be had with mullet, but 3 Sisters (as Kent mentioned) as well as beyond, into "Jan Bruin" bay and up to the point toward Kleinemonde is good. Also, drive to Kleinemonde East and walk East up the beach toward the Clayton Rocks... All is very fishable (particularly the Wreck... About 2.5km along the beach). Look for holes... No need for long throws. Good Kob, Grunter, Steenbras as well as ineds.
Lighthouse also used to have great fishing (further east toward Fish River)... Fish River point also great for ineds.