How to be a Wild Trout Detective: Part II

Part I Here

Digging Deeper

Once you've thoroughly searched the web for mentions of wild trout streams in your state (see Part I), you should have a solid list of streams. But they might be too far away for easy travel or they might be popular destinations, and therefore crowded. What can you do to find more streams?

Fish Surveys

Many state fish and game departments perform electroshocking surveys on streams. Oftentimes, they publish reports which can be found online. Massachusetts publishes them as part of "Water Quality Assessments" (see Part I for link) which examine several water quality metrics, including fish species. The best trout streams are dominated by trout, with lesser numbers of blacknose dace and/or slimy sculpins. If a stream has few trout relative to other species and/or warmwater species present, the trout fishing may be marginal. There's still a possibility that they hold nice trout though, as some of the biggest trout in a system are often found in marginal water, so don't count this kind of stream out entirely.

Water Quality

Water Quality data is readily available in most states. While it is conveniently paired with fish survey data in MA, it is often reported separately. The two most important metrics for trout are temperature and pH.

A trout stream should ideally never go above 20 C (~68 F), but trout can survive higher temps if they are infrequent. Some streams have springs that serve as cold water refuge for trout in streams that are otherwise too warm, so warmer streams can still hold trout. Regardless, look for streams that stay sufficiently cold first - they are most likely to have a large trout population.

The ideal pH for a trout stream is between 7 and 8. Aquatic insects thrive in these conditions, giving trout a larger food base. Streams with pH between 7 and 8 are also more likely to contain brown or rainbow trout, which have a lower tolerance for acidity than brook trout, which can survive in streams down to pH 5.0. Streams that flow through limestone or other carbonate based rock often have ideal pH, while streams that flow through granite are often acidic, especially in areas affected by acid rain.

Aquifers (See Full Post Here)

Aquifers provide cold ground water to streams, keeping them within the ideal temperature range for trout. Because aquifers are often a source of drinking water, they are well-documented and often available as map overlays (see MA Oliver from Part I). All other things being equal, streams that flow through/near aquifers will usually be better trout habitat than streams away from aquifers.

Gradient

In warmer, low elevation areas, like Eastern MA, high-gradient (steep) streams often provide the best trout habitat, as they don't have much time to warm as they flow quickly downhill. Some lower gradient streams get too warm in these areas, but those that don't provide excellent trout fishing. Lower gradient streams are often better in high elevation areas, as they are one of the few areas the water can slow down enough to form the deep pools needed by large trout.