Bobber Lure is the default type of Lure that appears in The Legend of Zelda: Twilight Princess.
The Fishing Rod Link receives from Colin's mother Uli (which crafted by Colin for Link) automatically comes equipped with this type of Lure and is the only lure that Link can use outside of the Fishing Hole. After casting is line into the water, the Bobber Lure will float on the surface and when the bobber's float dips underwater at least half of its total length, it is a signals that Link has a bite on the end of his line. However it should be noted that if Link casts in water with a current (such as rivers and near waterfalls), the Bobber's float may not stand straight up, making it harder to tell when Link gets a bite.
Interestingly, this lure is capable of catching every catchable fish in the game (from Greengills to young Hylian Loach), even forbidden fish such as the Bomb Fish and Skullfish. If Link catches a Bomb Fish, he use it to refill his stock of Water Bombs. Link can also equip this Lure with bait such as Bee Larva and Worms.
Link can use the Bobber Lure in any body of water near land or a platform. He can also Bobber fish at the Fishing Pond for free.
Later in the game, after Link obtains the Coral Earring (which is automatically attached to the Bobber Lure after obtaining it) from Prince Ralis, it will be equipped to the Bobber Lure as a Fishing Hook allowing Link to catch Reekfish. Interestingly, in order to catch the Sinking Lure by Bobber fishing, Link must have obtained the Coral Earring for his Bobber Lure.
In addition to fish, Link will occasionally snag items such as Boot, Empty Can, Wheel, Twig, and even a Bag of Rupees while Bobber fishing. At the Fishing Hole, Link can Bobber Fish to obtain an empty Bottle and the aforementioned Sinking Lure.