In the wave-swept waters off the Pacific coasts, the giant kelp, Macrocystis pyrifera, both shapes its environment and is shaped by it. Kelp forests are some of the most important ecosystems on Earth, yet these vibrant, underseas environments are difficult to appreciate from land, or even the ocean's surface. This work explores methods to model and animate kelp forests in software, bidirectionally coupling a fluid simulation based on Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) with a model of kelp fronds defined by articulated rigid bodies, with appropriate boundary conditions for the simulation region.