The statute and rule state that you must OFFER a helmet if your trip will go through Class III whitewater. You may offer for rent or sale, and it may be verbal or in writing. It is NOT a requirement to wear them.
(1) A person who acts or offers to act as an outfitter and guide using boats to carry passengers on the waters of this state shall:
(e) On any section of waters rated as class III or higher on a commonly accepted scale of river difficulty, rent, sell or otherwise make available to all passengers helmets that meet the standards established by the board by rule.
Safety and Equipment Requirements for Whitewater River Outfitter and Guides
(4) To meet requirements of ORS 704.070(1)(e), helmets made available to passengers must meet the CE EN (European Committee for Standardization) 1385 standard. Helmets are considered to be available when the Outfitter and Guide:
(a) Sells or rents helmets, or otherwise causes the availability of helmets, at or near the watercraft rental location; or
(b) Provides notification to potential customers that Class III or higher waters will be encountered and allows the customer to decline the offer of a helmet verbally or in writing, or to otherwise obtain a helmet for use during the activity.