Lake Acuity (Japanese: エイチ湖Eichi Lake) is a location in the Sinnohregion, and part of the Alabaster Icelands in the Hisui region. At the center of the lake, there is a cave that is named Acuity Cavern, which is home to the Legendary PokémonUxie, the guardian of the lake and the Being of Knowledge.
According to Volo, the lake contains seawater, though nobody knows whether this is due to something in its geography or because of a Pokémon.
An AlphaHisuian Zoroark can be caught during Mission 16: "The Trial of Lake Acuity", which becomes available after completion of Mission 13: "Disaster Looming". Once defeated, Zoroark does not respawn. It is coded to never be Shiny.
Uxie can be caught during Mission 21: "The Plate of the Lakes", which becomes available after completion of Mission 20: "The Researcher of Myths". If fled from or knocked out, it respawns immediately without leaving the area. It is coded to never be Shiny.
In The Needs of the Three!, it was explained that Lake Acuity, and indeed all three of Sinnoh's lakes, are the entrances to another world where the lake guardians reside, although they do not live in the lakes themselves.
The three were almost immediately confronted by CommanderJupiter, who was easily able to defeat them, despite two of them being Gym Leaders. After the Galactic Bomb was detonated at Lake Valor in Tackling Tangrowth, Uxie emerged from the Acuity Cavern and was quickly captured by Team Galactic.
Lake Acuity appeared in The Battle Rages On and A Novel Test!!, where Mitsumi battled and defeated Jupiter there. However, by bringing up Mitsumi's past as a Team Galactic member, Jupiter was able to throw off Mitsumi and shock Jun, allowing her to take the latter hostage. She then contacted Cyrus, who ordered her to bring Mitsumi to the Team Galactic HQ. Mitsumi refused at first, but Cyrus was able to change her mind, and she reluctantly left with Jupiter, leaving Jun behind in the snow, where he was later found by Hareta.
Lake Acuity was introduced as a Stadium card in the Pokémon Trading Card Game during the English Sword & Shield Series (the Japanese Sword & Shield Era). It was first released in the Japanese Dark Phantasma subset and the English Lost Origin expansion, with artwork by Oswaldo KATO. It makes all Pokémon that have any Water or Fighting Energy attached take 20 less damage from attacks from the opponent's Pokémon.
At each of Sinnoh's lakes, a TM can be found containing a powerful move of a different type. Lake Acuity's TM is the Ice-typeTM14 (Blizzard).
Lake Acuity is the only lake in Sinnoh where Team Galactic isn't fought. Instead, Barry fights Jupiter, losing and vowing to become stronger.