Guideline values have not been established for the cyanobacterial toxins in the United States, however several countries outside the US do have various working values. These range from advisory levels to maximum allowable values (MAV). The levels for recreational contact are much higher than the allowable levels for drinking water. Most values are in terms of actual toxin concentrations, some countries also have advisory levels in terms of cell numbers also.
For more information, see "Current Approaches to Cyanotoxin Risk Assessment, Risk Management and Regulations in Different Countries" compiled and edited by Ingrid Chorus.