 After a "bitter" campaign Plaid Cymru lost their remaining two ward seats to the Labour Party, with sitting Labour councillor Iona Gordon topping the poll.Plaid Cymru councillor Gwenllian Lansdown resigned her seat in January 2011 after six years representing Riverside, because she had moved from Cardiff to live in Powys.The resulting by-election took place on 3 March 2011, which was won unexpectedly by the Labour candidate, Iona Gordon.