Just a quick question before considering an answer: Are you saying this dugout is large enough to support nesting geese and ducks?.....Like a quite large large stock pond? Thanks....
Edited to add: Not at this point a recommendation, but additional information to aid in decision making. I was surprised to see citric acid once again emerge in the larger forum discussion. Starting from here --
https://www.epa.gov/pesticide-registration/antimicrobial-products-registered-disinfection-use-against-avian-influenza -- I tunneled into the list of registered anti-microbials, some of which have claims of efficacy against Avian influenza. The rather large database found here --
https://www.epa.gov/pesticide-registration/epas-registered-antimicrobial-products-effective-against-avian-influenza -- is heavily populated by the usual suspects, -- bleach, hydrogen peroxide, quaternary ammonium, etc. But then it lists several registered products that are mostly 99% citric acid. It is *possible* that having some solutions of citric acid around not only to wipe away splash points on surfaces, but also as a pre-rinse of any veggies would greatly reduce some of the worries here. Finally, although there would be additional costs involved and may provide information that you will have to make a judgement call with once received, this service at the University of Saskatchewan (can't recall just now if this is your province) might be able to do a sensitive test for presence of avian influenza, [
https://pdsinc.ca/services/molecular-diagnostics ] although you probably would have to work out a sampling procedure over the phone with them. They appear to be more geared towards animal/livestock testing but clearly have influenza A in their testing. If i'm wrong about the province, most of the major Uni's will have testing facilities like this. Hope this is of some help....