River deltas along the circumpolar arctic coast are lake-rich and poorly understood ecosystems, set in a region expected to change rapidly. Over the past 30+ years annual river-to-lake connection times in the Mackenzie Delta have lengthened (>30 days) in the lowest elevation lakes and may have shortened in the highest elevation lakes, respectively via sea level rise and declining effects of river-ice breakup. Lengthened connection times indicate summer low-water levels in the delta have increased by an amount (0.3 m) equivalent to three times local sea level rise (0.1 m) over the same period. Such an amplification effect of recent sea level rise has been completely unexpected and may be a result of enhanced storm surges in response to receding arctic sea ice or coastal backwater effects on the river flow. Shortened connection times are consistent with other work showing a decline in river-ice breakup effects, an important control on annual peak water levels.