Assuming you are asking about sprint speed kayakers can hit in short bursts, the answer is they can go extremely fast. In competition, kayakers will often reach speeds around 10 miles per hour in short 200 meter bursts. While this may not seem very fast, consider that professional sprinters can only run around 28 miles per hour and Olympic athletes swim at around 2 miles per hour. Kayakers therefore reach speeds similar to those of professional runners and swimmers but do so in a sitting position using only their arms for propulsion.
Some elite level kayakers have been clocked going even faster than 10 miles per hour. One such kayaker is Michael Foster who set the world record for the 200 meter sprint in 1999 with a time of 36.08 seconds. This corresponded to a speed of approximately 11.6 miles per hour!