Aquatic Pest Control
Water is the most regulated site
Aquatic pest control carries the tightest rules of any category. The product must be registered for aquatic use, and the surfactant must be aquatic-labeled as well - most ordinary surfactants are illegal in water. In New York, aquatic applications also require a DEC permit in addition to certification, and some waters involve additional agencies or conditions.
Know the targets: algae, submersed, floating, and emergent plants, and fish or shellfish pests. Understand treatment timing, dissolved oxygen, and nontarget risk. Decaying vegetation consumes oxygen, so a large kill can cause a fish kill. Buffers protect open water and wetlands from drift, and many labels restrict water uses (drinking, irrigation, swimming, livestock) for a stated period.
Traps: using a terrestrial herbicide in a pond because 'it kills plants'; treating an entire waterbody at once; ignoring the water-use restrictions on the label; and forgetting downstream users, domestic wells, and irrigation intakes. Permit conditions may limit acreage, season, or method - read them as if they were label text.
Rule of thumb: for algae and dense submersed plants, treat in sections - commonly about one-third of the area at a time - waiting for oxygen to recover before the next section, as the label and permit allow. Watch for dead-fish or off-color water after treatment and be ready to aerate or stop.