tl;dr your decomposers, fish, microbes, and clams would all be adversely affected. This will probably be blamed on the curse, though.
This is a study on the effect of silver nanoparticles on ecosystems. Here’s my quote:
Minimal variation in the size and surface charge of AgNP indicated that nanoparticles were rather stable during the experiment. Five days of exposure to 0.05 and 0.5 μM AgNP in microcosms shifted bacterial community structure but had no effect on a suite of microbial metabolic activities, despite silver accumulation in the decomposing leaf litter. After 25 days, however, a broad range of microbial endpoints, as well as rates of litter decomposition, were strongly affected. Declines matched with the total silver concentration in the leaves and were accompanied by changes in fungal and bacterial community structure.
Basically, what it is saying is that prolonged exposure to silver nanoparticles causes significant change in decomposing bacteria and fungi, and that silver lasts a long time (minimal variation on size) By 25 days of exposure, metabolism and decomposition rates were affected, and by 5 the structure of colonies had changed. Perhaps after longer term exposure they might die.
Given that silver powder is similar to silver nanoparticles, I would expect similar effects to all that drink from the tainted water. Decomposers would be affected at the very least, and since they are an integral part of an ecosystem, I would expect long term adverse effects.
Even better, I found a Wikipedia page on the impact of Ag0 on environment: https://en.wikipedia.org/wiki/Environmental_impact_of_silver_nanoparticles#Toxicology_in_aquatic_environments
Basically, it says that it is extremely adverse to microbes. The microbes get eaten by bigger things, like fish.
... can accumulate and block the regulation of Na+ and Cl− ion exchange within the gills of fish, leading to blood acidosis which is fatal if left unchecked.
As fish eat phytoplankton, the silver accumulates within their circulatory system, which has been shown to negatively impact embryonic fish, causing spinal cord deformities and cardiac arrhythmia. The other class of organisms heavily affected by silver nanoparticles is bivalves.