Megan Bloom scored 19 points and Kate Kraft picked up eight steals as the Chieftains won their 13th game of the season.
Columbia River improved to 13-4 with a win in its final non-league game of the regular season.
Marion Lilly added 14 points.
Teagjam Cowles had seven points and a team-high eight rebounds. Bloom added six rebounds.
Columbia River returns to 3A GSHL play on Friday against Prairie.
COLUMBIA RIVER 54, TUMWATER 40
COLUMBIA RIVER — Ellie Furth 0, Amara Moore 0, Marion Lilly 14, Kate Kraft 4, Teaghan Cowles 7, Holli Jo Chose 4, Gabrielle Collins 3, Katie Kolbe 0, Megan Bloom 19, Maddy Kessi 0, Emma Fisk 3. Totals 18 (4) 14-22 54.
TUMWATER — Schneider 12, Kelly 0, Smith 4, Hare 4, J. Armstrong 10, Burquist 8, Rodriguez 2, Rossman 0. Totals 15 (1) 9-12 40.
C. River 14 17 15 8—54
Tumwater 6 14 12 8—40
JV — River 45-41 C — River 38-21