Mission
Rivers are the least observed water we manage.
We can see a lake from a satellite and an ocean from a mooring. A river in spring is opaque, loud, and moving — and almost everything we believe about the fish in it comes from a few nights of sampling a year.
The gap
Decisions about rivers are made constantly and at scale. Dams are relicensed. Barriers come out. Seasons are set, recovery targets are written, and hundreds of millions of dollars of restoration go into channels on the strength of what is, in most cases, a very thin observational record.
The limit is not that people lack the will to measure. It is that the measurement is genuinely hard. A river you cannot see into resists cameras and nets alike, the fish that matter most are often the rarest, and the sampling windows are short, cold and at night. So the record stays thin, and the uncertainty gets absorbed quietly into decisions that deserve better.
What we are trying to change
Acoustics can watch a channel continuously. That capability has existed for decades; what has limited it is that somebody then has to read the result, and reading it is expert, slow, and unrewarding work — mostly the labour of rejecting things that are not fish.
Thalweg exists to make that reading cheap enough that continuous measurement becomes the ordinary way to monitor a river, rather than a special project. Not to replace the biologist — to hand them a season already sorted, so their judgement goes where judgement is actually needed.
Passage facilities and relicensing carry counting obligations that run for years, in water no camera can survey.
Take out a barrier and the question is immediate and unavoidable: did the fish respond? That needs a before and an after, across whole seasons.
Run timing across an entire migration, rather than a handful of sampled nights, is a different quality of evidence.
Built to be checked
An instrument is only worth what its numbers are worth. Every output Thalweg produces stays traceable back to the echo it came from, so a result is never a verdict handed down by a black box — it is a claim with a picture behind it.
That is the standard fisheries science already holds itself to, and it is the reason this was built by someone who has to defend the numbers in front of a committee.