Can light aircrafts with no retractable landing gear make an emergency water landing?
Can they land on water? Yes.


  Most pilots contend that the ideal airplane for ditching is a low-wing aircraft with landing gear retracted. Statistics, however, do not substantiate this. Aircraft geometry and landing gear configuration do not appear to affect survivability appreciably. (Source.)


If you try this Google search, you'll find plenty of high-wing fixed-landing-gear water/sea/ocean landings. The outcomes for the occupants vary.

In Oct 2015:


  The [Cessna 152] was ditched in the [waters off Grand Bahama]  after experiencing a technical failure. Both trainer pilot and trainee remained unhurt.


In Dec 2013:


  The Makani Kai Air Cessna 208B Grand Caravan impacted ocean waters shortly after takeoff from Kalaupapa Airport (PHLU), on the island of Molokai in Hawaii. The airplane sustained substantial damage. The pilot and two passengers were seriously injured, one passenger was fatally injured, and five passengers received minor injuries.




Related: What are the risks in landing on a beach vs. shallow waters?