yamunāra bhrame - by mistaking for the Yamunā; prabhu - Śrī Caitanya Mahāprabhu; dhāñā calilā - began to run very swiftly; alakṣite - without being seen; yāi' - going; sindhu-jale - into the water of the sea; jhāṅpa dilā - He jumped.

Mistaking the sea for the Yamunā, the Lord ran swiftly and jumped into the water, unseen by the others.