River King: Mystic Valley
North American box art
Developer	Marvelous
Publishers	NA: Natsume JP: Marvelous EU: Rising Star Games
Producers	Hikaru Nakano Keiichi Ajiro
Programmers	Fumio Saito Souichi Ashida Ken Otani Takashi Horie
Artist	Igusa Matsuyama
Composer	Riyou Kinugasa
Series	River King
Platform	Nintendo DS
Release	JP: June 28, 2007 NA: April 29, 2008 EU: October 16, 2009
Genres	Fishing, role-playing
Modes	Single-player, multiplayer

River King: Mystic Valley, known in Europe as Harvest Fishing and in Japan as Fishing Master of the River: Valley of Sunlight, Song of the Stream,^[a] is a 2007 fishing role-playing video game developed by Marvelous for the Nintendo DS. It is, currently, the most recent installment in the River King series, and follows an unnamed male protagonist as they explore a valley in order to find a fish, known as "The River King", that can cure their sister from an endless slumber.

River King: Mystic Valley is a fishing role-playing video game.^[1] The player controls an unnamed male protagonist through a valley as they attempt to find a fish, known as "The River King", in order to cure their sister from an endless slumber.^[2][3]

An entry of the River King series for the Nintendo DS was first announced to be in development on August 2, 2004.^[4] The game would later be shown off in Japan at the 2006 Tokyo Game Show convention,^[5] and in North America at the E3 2007 trade show under the title River King: Wonderland.^[6][7]

The game garnered "mixed to negative" reception, according to review aggregation website Metacritic.^[8][b] Generally, reviewers viewed it as a title that lacked depth in its gameplay.^{[9][1][10][11]}