They have to eat. They’ll hunt for food via senses, probably including scent. Alchemy and medicine and hunting can let us lay a trap. The snake eats the bait, and either poison or explosives do the job.
What’s the payoff?
- Public gratitude for eliminating a major hazard - this might come in the form of Value from individual merchants, or reputation with factions who do a lot of overland shipping (or who use boats and are attacked by water snakes?)
- Notoriety from the Lizard Cult for killing a symbol of their god
- If we haul the corpse into a clearing and make an announcement or post a manifesto, it can be seen as a defiant challenge against the power of one or more factions - “we can take on big scary threats like this, and we can take you on too”