Since approximately 130 A.D. the bed of the Waikato River, in its lower reaches, has been raised 20 to 30ft - most likely by an amount closer to the latter figure. This represents an average of about 1ft every 60 years. Of the causal factors discussed, it is concluded that man-caused erosion is the main contributory factor but, as sea level may have been 10ft lower during 130 A.D., a rise of this amount would no doubt be another major cause.