Anytime its tail swipe strikes a foe, the foe must succeed in a DC 20 Strength-based saving throw (or, if using old-school saving throws, a flat save versus Paralysis/Petrification). Failure indicates the target is knocked ten feet and falls prone. The foe must use half his action economy to regain his feet.
Steam Breath (Recharge 5-6). The dragon turtle exhales scalding steam in a 60-foot cone. Each creature in that area must make a DC 18 Constitution saving throw (or save versus wands), taking 52 (15d6) fire damage on a failed save, or half as much damage on a successful one. Being underwater doesn't grant resistance against this damage.
The only chance of finding treasure is if confronting the dragonturtle in its lair — which isn't as likely as an open-water encounter.
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