Our house is quite near a water way as the crow flies, but the elevation and location mean it's fine. However, there are a few insurers who just do a how many meters appraisal. Which rules them out. It's just the way a particular insurer sets their criteria.
Maybe it wasn't a risk and now they're using different data which classifies it otherwise? I dunno. Can you check the data they're using somewhere?
Maybe it's a predictive thing based on how we're fucking up the planet.