* Water availability: Underwater plants are adapted to live submerged in water. They rely on the water for nutrients, support, and for photosynthesis. A forest environment, while containing water, doesn't provide the constant submergence that underwater plants need.

* Sunlight: Underwater plants need specific amounts of light for photosynthesis, which varies based on water depth and clarity. Forest environments, with their dense canopy of trees, block out most sunlight, making it difficult for underwater plants to thrive.

* Root structure: Underwater plants have root systems designed for anchoring in sediment and absorbing nutrients from the water. These roots are not adapted to the soil conditions and water availability found in forests.

* Gas exchange: Underwater plants have evolved ways to obtain oxygen from the water. In a forest, they wouldn't have access to the same levels of dissolved oxygen, making survival difficult.

In summary: Underwater plants are highly specialized for their aquatic environment and cannot survive in a forest.