We are on the edge of a small coastal wetland. Permanent stream, sedges and rush. No frogs are present (heard). Would it be wise to buy tadpoles for release? According to a neighbor frogs used to live in the area.
Lincoln County Oregon frogs
The best thing you can do is look at what might be causing the decline.
Animal populations fluctuate over time and it's a normal part of nature. So what you are seeing might be natural and they could bounce back on their own. It could also be a result of something you are doing on your property or your neighbors are doing. Frogs are susceptible to pesticides because they absorb chemicals through their skin. So reducing pesticide use will create a healthier habitat with more insects for them to eat. But the biggest problem for frogs is habitat degradation. Land development by humans means a loss of habitat for frogs. Roads are particularly problematic as frogs must move from feeding grounds to breeding ponds each year.
I do not know what frog species you have or what your situation is, however you can help boost your population by adding habitat in your own yard. Frogs need places to hide from predators and they need places to go in hot temperatures."
We agree with Michael that the best idea would be to try and improve your habitat to get native frogs to move in on their own. There are several Extension resources on frog habitat and conservation that you may find helpful in the following link at the bottom of the page: https://extension.oregonstate.edu/outdoors-environments/wildlife/can-i-purchase-frog-eggs