What evidence shows that the Indus civilization traded by river and sea?

Evidence for river and sea trade in the Indus civilization is supported by both archaeological findings and the discovery of specialized maritime infrastructure.123

Maritime and Riverine Evidence

• Lothal Dock: The most significant evidence for sea trade is the large brick basin discovered at Lothal, which is widely interpreted as a dock. It featured a sluice and spillway system to manage water levels, and heavy pierced stones found nearby are believed to have served as anchors for ships.43
• Watercraft Models: While many terra-cotta models of boats found in the region appear designed for river travel, a specific model discovered at Lothal included a socket for a mast and eye holes for rigging, suggesting a more seaworthy vessel capable of navigating the sea.3
• Trade Artifacts: The presence of Indus seals in Mesopotamia and the discovery of a "Persian Gulf" type seal at Lothal provide strong evidence of maritime commercial networks connecting the Indus region with ports in the Persian Gulf and beyond. Literary records from Mesopotamia also mention trade with Meluhha (the Indus region), noting that vessels sailed directly to Mesopotamian ports during the Akkadian period.12