In this paper, the first water-to-ice (W2I) wireless optical communication (WOC) system model is proposed and verified by laboratory and field experiments. The Monte Carlo (MC) approach is used to simulate the optical characteristics of ice and water, resulting in the channel impulse response and received optical power (ROP) distribution. The simulation results demonstrate that the substantial absorption and scattering of the ice and ice-water interface significantly affect the cross-medium communication. A comparative study in the laboratory validated the channel characteristics obtained from the simulation. Following this, a W2I WOC system based on photomultiplier tubes (PMTs) was established. Using the maximum ratio combining (MRC) technique, a net data rate of 400 Mbps was achieved in a 1-m laboratory tank, and a net data rate of 320 Mbps was achieved across a 1-m transmission distance in the reservoir. To reduce the computational complexity and realize practical system deployment, the orthogonal matching pursuit (OMP) approach is employed to compress the equalizer. The number of kernels in the Volterra equalizer is reduced by 36% in the laboratory experiment and 36.9% in the field experiment, respectively. The results of this study can serve as a reference for future deployment of W2I WOC systems.