I would say that it would be 5% of infection right now, which appears to be about the limit of what we see on juvenile salmon during their first few months of marine life with Lepeophtheirus salmonis, which is the salmon louse.
Now, there are other species of sea lice out there that do tend to be more prevalent during this phase of their life history, but the salmon louse is the species that is the problem, and the baseline levels for this species are approximately 5% in areas without salmon farms.