In April of 2000, Ishikawa Rika was chosen to join Morning Musume as part of the fourth generation, alongside Yoshizawa Hitomi, Tsuji Nozomi, and Kago Ai. Soon after joining, both Ishikawa and Kago were added to the subgroup Tanpopo to replace Aya Ishiguro, who had graduated from the group and Hello! Project the previous year.
In 2001, Ishikawa was "loaned" to the group Country Musume to form Country Musume ni Ishikawa Rika , even though she wasn't a Hokkaido native like group members were intended to be. Initially she was supposed to release only one single with Country Musume before another Morning Musume member was rotated into the group, but because sales went up with the addition of Ishikawa, she worked with them until 2003.
In 2003, Morning Musume was split into two groups and Ishikawa became a part of Morning Musume Otomegumi, the more rock-influenced group of the two. Later, in 2004, she partnered with Michishige Sayumi to form EcoMoni, a group intended to promote ecological awareness at various events.
In August of 2004, Ishikawa became the leader of a new group, v-u-den, with newcomers Miyoshi Erika and Okada Yui. After graduating from Morning Musume on May 7, 2005, she focused full-time v-u-den until their disbandment on June 29, 2008.
Ishikawa has been featured in seven solo photobooks, and she also had her own radio show, Chanchaka Charmy.
In September of 2006, Ishikawa starred in the big-screen movie Sukeban Deka Codename Asamiya Saki (a.k.a. Yo-Yo Girl Cop), opposite fellow Hello! Project member Aya Matsuura. She played the renegade villain, Special Detective Akiyama Reika. The remaining two v-u-den members, Miyoshi Erika and Okada Yui, also had parts in the movie.
In 2007, Ishikawa was added to Ongaku Gatas, a group consisting of members from Gatas Brilhantes H.P., the Hello! Project futsal team. After the announcement in January of 2008 that v-u-den would disband, it was expected that Rika would shift her focus to Ongaku Gatas. They have released a total of three singles and an album, but their future is uncertain after the announcement of the graduation of Elder Club from Hello! Project, which includes both Ishikawa and Ongaku Gatas. The graduation will take place on March 31, 2009, at the concert Hello! Project 2009 Winter Elder Club Kouen ~Thank you for your LOVE!~.
On October 12, 2008 it was announced that she is paired up with fellow ex-Morning Musume member Hitomi Yoshizawa in the new unit Hangry & Angry in collaboration with a Harajuku fashion store of the same name. Hangry & Angry will be making their first United States performance at Sakura-Con in Seattle, Washington in April 2009.
It was announced on October 19, 2008, on the official Hello!Project website, that Ishikawa will graduate from Hello! Project along with the rest of Elder Club on March 31, 2009. Ishikawa joined the newly formed group, "Dream Morning Musume" in 2010 alongside other former Morning Musume members.