British rowers Helen Casey and Tracy Langlands have failed to reach the final of the lightweight double sculls.
The duo could only manage fifth place in their semi-final heat, which was won by defending champions Romania.
And Britain's men found life just as difficult in their semi-final heat of the quadruple sculls.
The foursome were way off the pace and suffered the huge disappointment of coming in last, with the Polish crew powering to victory.
Elsewhere for Britain, three crews were in 'B' final action, with two of them ending their Olympic campaigns on a high.
The men's pair of Rick Dunn and Toby Garbett produced a storming finish to overhaul long-time leaders Italy on the line and claim victory by just four hundredths of a second.
And the men's double scull also produced a fine display as they led from the halfway point through to the finish to hold off the German crew by two-tenths of a second.
Meanwhile, Ian Lawson finished fourth in the single sculls.