The Attanagalu Oya (Sinhala: අත්තනගලු ඹය) is a river in Gampaha District, Sri Lanka.

[1][2] The length of the river is approximately 76 km, with a drainage basin of 727 km2.

[1][3][4] It originates in Galapitamada area in Kegalle district and drains into the Negombo Lagoon as the Dandugam Oya.

The river originates from lower peneplains of Kegalle District in Galapitamada area.

Close to its mouth it is also joined by Ja-Ela which is a diversion of the Uruwal Oya.