Abstract The Siple Coast region of West Antarctica is known for its fast flowing, topographically unconstrained ice streams that evolve due to subglacial conditions. In this work, we analyze the nature of the Siple Coast subglacial hydrologic system and its interactions with the ice sheet using two‐way coupled subglacial hydrology and ice flow modeling. Our modeling is consistent with observations of a water saturated till layer underlying the Siple Coast ice streams. We find that future thinning of ice upstream of Ice Stream B can lead to a hydraulic potential low that promotes water amalgamation and drainage through the ice stream, leading to pulses in ice motion. The inclusion of an ice‐dynamics driven variable melt rate and the alteration of glacier driving stress due to subglacial lake geometry lead to stabilized motion of Ice Stream B. These feedbacks demonstrate the importance of coupled modeling for projecting the evolution of ice dynamics.