Soft robots are being increasingly developed and deployed for underwater applications such as exploration, monitoring, and rescue owing to their innate compliance, mechanical and chemical stability, and waterproof properties. However, they are still predominantly manufactured using silicones and acrylic elastomers, which pose environmental risks due to their limited biodegradability. To tackle this issue, we present a method for manufacturing water-resistant, liquid-driven soft actuators made from a novel type of konjac glucomannan that is plant-derived, insoluble, and edible. The material offers impressive stretchability, reaching up to 67.2% of its initial length, surpassing previous related work, and withstands over a 1000 cycles of tensile stress. Using this material, we develop soft actuators that can bend up to 47.1 °, and the maximum blocking force of 0.1 N is achieved with a pressure input of 20 kPa. We also evaluate a gripper that is capable of grasping various objects underwater. In essence, this paper introduces a sustainable and environmentally friendly alternative to conventional soft robotic materials, paving the way for innovative and eco-conscious underwater applications. The utilization of edible, water-resistant materials like konjac provides a promising solution to reduce pollution and mitigate negative environmental impacts associated with traditional underwater soft robots.