The very elongate body is a uniform dark grey above, lightening to yellowish off-white on the sides and pure white below.

Like all lampreys, these fish lack paired fins and possess a circular sucking disc instead of jaws.

The teeth are sharp and these fish can be told from the rather smaller brook lamprey (Lampetra planeri) by the fact that the two dorsal fins are more widely separated.

[7] An assessment for the Baltic Sea published in 2014, however, classified the river lamprey as Near Threatened in this region, supported by the IUCN's 2024 classification.

[4] As ammocoetes, identification of these animals beyond genus level (Lampetra) is difficult because of their close similarity to brook lamprey.