The heart of Nashua is poison.
The central marshlands formed over millennia as mineral-rich waters from the Dreske Gemalis mixed with organic decay in the lowland basins. The result is an ecosystem saturated with natural toxins: arsenic compounds in the soil, sulfurous gases bubbling from stagnant pools, and a food chain where nearly everything has evolved to be venomous, poisonous, or both.
The Ix'Vasyla did more than adapt to this environment; they weaponized it. Their scales resist toxins that would kill most warm-blooded creatures within hours. They know which pools are merely unpleasant and which will dissolve flesh. They've cultivated the deadliest plants and bred the most venomous serpents. To invade the marshes is to fight the Ix'Vasyla and the land itself.
The marshes are navigable only by those who know them. Channels wind between islands of semi-solid ground, but the routes change with seasons and floods. The Ix'Vasyla travel by shallow-draft boats, by vine-rope bridges hidden in the canopy, or simply by swimming through waters that would poison their enemies. Outsiders who try to follow find their boats dissolving, their guides dead, and the way back vanished.