We would need to see the wasp in question to provide the best answer; however, there are few products available that manage either of the two possible suspects well.  The most likely culprit you are having fly towards workers are the cicada killer wasps.  There are no treatments that work well and there will never be any developed that target this beneficial insect.  This insect is a non-aggressive beneficial wasp that enjoys open, sunny, well drained locations to build its underground oviposition chambers.  The more sparse the vegetation the better.  Males typically fly at people and dogs of all ages and sizes, but they are unable to sting since they do not have stingers.  Females focus on digging the oviposition chambers underground and do not fly at people or pets.  They fly to trees to acquire cicadas for their offspring and this is all.  I have dug up their nests previously and had the females crawl up and down my legs while doing so and have never been stung.

If you seen an entrance to one of these underground chambers (one wasp uses it, there isn't a hive) insecticidal dust could be used but this type of treatment is seldom effective.  The insecticidal dust is the best insecticide option and it isn't very good.

The other option could be European hornets that are flying around; however, they typically are cavity nesters of sorts (hollows of trees, voids in houses, etc...) and are often found in wooded areas.  The only effective method to manage these is to remove the nest which can be difficult to locate in a landscape unless you are able to follow them to their nest.  This wasp is capable of flying at night so caution should be used when nest removal is desired.  A better option may be to have a professional deal with the hornet nest if you know where it is located.  European hornets are important beneficial predators in the landscape because they consume a variety of caterpillar and sawfly pests throughout the summer.

The removal of either type of wasp will be challenging if they are near the pond because the products available to use probably have restrictions for use around or near water due to toxicity to aquatic animals.  Cicada killers that are flying at people are almost always males and are unable to sting; consequently, tolerance is probably the most environmentally safe option.  Females rarely, rarely sting because they are not aggressive wasps.  European hornets would be more of a concern but are difficult to locate because of hidden nests.  Yellow jackets could be another possibility but since they are often ground nesters they are also difficult to treat.  It is difficult to provide sufficient recommendations (although there are not many good ones for what you describe) without seeing the insect itself.