Unfortunately Lesser Celandine (the other common name for Fig Buttercup) is rampant in many watersheds and public (and private) lands; difficulty controlling spread is one reason it's an invasive species. Public land managers do what they can with the limited resources they have. It sometimes is almost futile to remove an invasive species swath without having a plan to revegetate the area with native species (or to allow what native plant seeds that might remain come up without competition from recolonizations of this or other invasives in the meantime). This necessity to keep monitoring a cleared site is one reason municipal organizations tend not to have enough labor or funding to tackle all the invasive plants present in a given habitat.

Glyphosate has been the recommended systemic herbicide ingredient, but some anecdotal reports indicate it might no longer be as effective as it once was. (It's hard to say what the exact reason is...environmental conditions that vary from year to year might be contributing factors to herbicide efficacy.) In such cases, a mixture using the active ingredient triclopyr might be more effective, particularly if either ingredient is combined with a spreader-sticker when being applied. (As long as the product label(s) allow, since not every formulation is the same. Spreader-sticker products help liquid herbicide sprays adhere to waxy and water-repellent leaves like celandine's. Their usage instructions will be on their own product label, and the products tend to be sold alongside pesticides at garden centers.)

Treatments with systemic need to be made before this weed has finished flowering. If applied too late, the plant is already beginning to shut down foliage for dormancy and the application will not be well-absorbed enough to take effect. Even a successful treatment one year would probably require a few years of follow-up spot-treatment for plants that regrow. Plus, if the source of an infestation, like an upstream colony of celandine, cannot be removed first or blocked from washing downstream, it may be a futile effort to clear one area if it will continually face recolonization pressure each year. (Applying herbicides yearly is certainly not a recommended or practical approach.)

There are select formulations of glyphosate-containing herbicides that are intended for use near open waterways and watersheds; otherwise, a warning on the label will caution the user about how far to stay from a water source to avoid contamination. It is probably not legal to treat public land with a pesticide unless you hold a certified applicator permit from the MDA and have permission from the county (or land manager) as well. Not all herbicide formulations, even if using the same active ingredients in the same concentrations, are legal to use in woodlands or natural areas versus other settings like home landscapes, nurseries, and so forth.

Perhaps Baltimore County has a program (or would develop one) like Montgomery County's Weed Warriors, which trains volunteers in invasive plant ID and removal techniques (without herbicide). Natural land managers can use such help with plant removal (and maybe native species replanting efforts too). We understand your frustration with seeing this invader smother natural habitats, but unfortunately there is no single or easy remedy once such an aggressive plant has taken over. Some weed removal efforts use goats (penned in so they consume all the foliage on the weeds, though they will also eat just about everything else too), fire (controlled burns by trained professionals), and other non-chemical means (steam weeder tools, etc.), but in this setting there will probably be few options outside of tedious physical removal and/or careful herbicide use.

Miri