The Toto Lake is a location from The Legend of Zelda: Breath of the Wild. It is located in the Lanayru Great Spring region of Hyrule in the province of Lanayru. It is located northeast of Zora's Domain and flows into South Lake Akkala in Akkala Highlands via waterfall. The lake is home to the ruins of an old Zora Temple partially submerged in the middle of the lake which holds a secret connection to the Hylian Champion Link's past heroism before the Great Calamity.
Flooded Temple Ruins
In the middle of the lake are some flooded ruins where Link can lift a metallic Treasure Chest by using the Magnesis Rune. The chest contains the Zora Helm which allows Link to perform the water-based Spin Attack.
History of the Zora: The Hero Who Defeated the Lynel
According to two worn Zora Stone Monuments (one is a duplicate) during the side quest "Zora Stone Monuments", the Zora Helm was apparently won by Link while fighting a Lynel that had threatened Zora's Domain and lived on Ploymus Mountain. However Mipha's Diary which gives an eyewitness account of Link's battle with the Lynel makes no mention of the helm, indicating the helm may have been awarded to Link as he defended Princess Mipha whom had followed him during his hunt for the beast forcing him to protect her when they were attacked and Link killed the beast with a Spin Attack using the Master Sword. Alternatively Link drove off the Lynel and acquired the Zora Helm in a separate incident from his and Mipha's encounter with the Lynel which lead Link to kill the beast. At some point the Helm was placed by the Zora within the temple in Toto Lake (as it was a Zora temple it is mostly submerged underwater like the Water Temple and Lakebed Temple) to honor Link's heroic deeds. However the temple along with the Monuments that recorded Link's heroism fell into disrepair during the century following the Great Calamity presumably do to the Zora Council of Elders blaming Link and Hylians for the Calamity and Mipha's death. The two monuments (one of which is in Zora's Domain) that reveal the Zora Helm's location, acts as a word puzzle Link can decipher. However this is an optional activity that has nothing to do with the "Zora Stone Monuments" side quest as the two monuments can be deciphered before the side quest itself or Link can stumble upon the Helm while exploring Toto Lake. Additionally the word puzzle must actually be solved by the player as their is no in-game method for doing so.
Toto Lake is home to several species of fish including Armored Carp, Hearty Bass, Hyrule Bass, Mighty Carp, Staminoka Bass, and Voltfin Trout. Sneaky River Snails also can be found along the lake's shoreline though it is best to hunt for them at night as they glow in the dark. Tireless Frogs also appear when it rains (which is all the time before Link and Sidon take on Vah Ruta and shutdown its water pumps) while Hot-Footed Frogs appear regardless of the weather though are more numerous when it rains though Link my find Tireless Frogs instead or vice versa.
Like many locations in Breath of the Wild, Toto Lake is named after a character from a previous game, namely the Zora band manager of The Indigo-Go's Toto. Toto Lake's distance from Lulu Lake and Mikau Lake may be a reference to him being away from his band at Zora Hall during the events of Majora's Mask.