The calculated distance (air line) between Jēkabpils and Daugavgrīva is approximately 79 miles respectively 126 kilometers.
By car or train, the actual journey to Daugavgrīva is certainly longer, as only the direct route (as the crow flies) between Jēkabpils and Daugavgrīva has been calculated here.
Air line (approximately)
126 kilometers
68 nautical miles