As a retired Volvo marine diesel mechanic, I agree with Brett, It is quite common on west coast of Canada, Had to deal with this problem many times on high speed crew boats, We would put in up to 3 large in line Racor filters with clear bowls so you can see the contamination,run boat change filters a couple of times if that did not help have the fuel polished[there are service trucks that come to you].
As Brett says only use high high volume fuel stations.
Easiest way is to try changing filters several times. Then think of options