If I wasn't in Ontario, I'd be game. I never knew German translating Fishing-Tour Guide was a possible profession. I am in the wrong field.
Unless they are from rural areas (like some of my fam over there) or are 40+ years old, they will probably have a working level of English. And be eager to learn more.
You could always learn some German? It's really close to English, shares many of the same words, most of the same letters/sounds, and if you know French, they share a lot of words too.
And for a fishing trip, you might need to learn like 50 words. Fishing is Angln -> basically angling. Water is Wasser.
Or download google Translate on your phone.