I tend to cut independent and documentary films some slack when it comes to CGI. After all, the films aren't high budgeted and you need to make some allowances for this. However, there is a bit of CGI in this film which is terrible...so terrible it looks like it was made in 2000 or earlier. It's a shame, as the CGI scenes weren't really needed...but you can't help but be taken aback by how primitive they are.
That being said...this is still a very good documentary. Its purpose is to discuss two major problems the Great Lakes faced back in the 1950s-60s...sea lamprays and alewives...two saltwater species that somehow made it into the freshwater lakes. Most of the film is about the lampreys and their devastating effect on lake trout and, to a lesser extent, Whitefish. How the US and Canada eventually managed to reduce their numbers and create a better fishery is the subject of the movie. It does not, by the way, talk about the polution in the lakes (which has also been significantly reduced) or the state of fishing apart from salmon and trout. You'd never know it, but the yellow perch, smallmouth bass, and walleye in Lake Erie, for instance, are doing extraodinarlily well. But I am not faulting the film...in the time they had they had to pick what to focus on most. These are other success stories that other movies can address.
Overall, it's a very good movie...well made and surprisingly interesting. And, a rare case where fisheries have made HUGE rebounds thanks to technology and a lot of hard work.