Either O. ovalis or O. ampliatus based on color and location; O. ovalis has the pale pattern broken up into 2 separate spots while O. ampliatus has a more or less continuous pale stripe from the shoulder to the apex. This one appears to have a continuous single pale stripe but it may be hard to say because of the encrustations on it. Elmids, and to a lesser extent some other aquatic beetle families often develop a algal/periphyton crust on their body surface as they age, which can make them difficult to identify. Scrubbing the specimen with a small fine toothbrush or sonicating it will help get rid of most of the surface crud.

I thought O. ovalis is synonymous with O. ampliatus