What hippos do
Hippos deployed under the Scheme perform a range of canal maintenance activities. The Canal and River Trust has described these activities as ‘effective,’ ‘difficult to predict,’ and ‘not how we would have done it.’
Dredging
Hippos move through canal systems with what the Canal and River Trust describes as ‘considerable authority.’ Sediment is displaced. Vegetation is removed. The canal is, by any reasonable measure, cleaner. The Trust has described the results as ‘difficult to argue with, aesthetically.’
The dredging process is not guided by any engineering specification. The hippo moves through the canal. The sediment moves out of the hippo’s way. The Trust has noted that this achieves results comparable to mechanical dredging, but ‘with considerably less paperwork and considerably more water displacement.’
A senior engineer at the Trust, who asked not to be named because ‘this is not something I expected to be discussing in a professional context,’ confirmed that hippo-dredged canal sections showed a 35-45% improvement in water flow within the first month. When asked whether this was sustainable, the engineer paused for several seconds and said, ‘The hippo seems to think so.’
Vegetation management
Hippos consume aquatic vegetation at a rate that the Environment Agency has described as ‘industrial.’ A single hippo can clear a 200-metre stretch of canal in approximately 3 days. The vegetation does not return for 6-8 weeks. The Environment Agency has described this as ‘concerningly efficient’ and has asked the hippos to ‘maybe leave some for the fish.’
The Trust has monitored vegetation regrowth in all trial areas. In Birmingham, the aquatic plant population was reduced to what botanists at the University of Birmingham described as ‘a polite suggestion.’ In Rochdale, vegetation was eliminated entirely and replaced with what the Trust has classified as ‘hippo-related turbidity.’
The Environment Agency has raised concerns about the ecological impact of total vegetation removal. The Trust has responded by pointing out that the vegetation ‘was going to be removed anyway’ and that the hippo ‘is simply more thorough than the contractor.’ The contractor, when asked for comment, confirmed that the hippo was ‘absolutely more thorough’ and that they were ‘not threatened by this at all.’
Bank stabilisation
Hippos press against canal banks. The banks become compacted. The technical term is ‘hippo-compaction.’ The Canal and River Trust has acknowledged that this is not a recognised engineering technique but has conceded that ‘it appears to work.’
The compaction process occurs when hippos exit and enter the water along the same route repeatedly. The weight of the hippo compresses the soil, creating a denser, more stable bank profile. Geotechnical surveys conducted after the Birmingham trial showed a 28% increase in bank density along hippo access routes.
The Trust’s engineering division has proposed adopting hippo-compaction as a formal technique. The proposal was rejected on the grounds that it ‘requires a hippo’ and that the Trust ‘cannot guarantee hippo availability on a project-by-project basis.’ The hippo was not consulted during this decision, which the Trust considers ‘standard practice for engineering matters involving large mammals.’
Deterrent effect
Unauthorised mooring has decreased in all trial areas. The Trust has not established whether this is due to improved canal management or the presence of a hippo. They consider the outcome ‘the same either way.’
In Birmingham, unauthorised mooring incidents fell by 87% during the trial period. In Wigan, they fell by 94%. In London, they fell by 100%, although the Trust notes that this may be attributable to the trial lasting only two weeks and the narrowboat community having ‘other concerns at the time.’
The Trust has not attempted to study the deterrent mechanism. A spokesperson confirmed: ‘We could investigate why people choose not to moor their boats near a hippo. We could also simply accept the results and move on. We have chosen the latter.’
What hippos do not do
For the avoidance of doubt, the Trust wishes to clarify the following:
- Hippos do not operate lock gates
- Hippos do not collect tolls
- Hippos do not fill in paperwork
- Hippos do not attend meetings
- Hippos do not respond to emails
- Hippos do not observe speed limits, because they do not have a speed
A hippo in the Birmingham Canal Navigations was observed approaching a form but appeared to lose interest. The form was later found in the canal. The Trust has classified this as ‘an administrative outcome.’
A hippo in the Rochdale Canal was observed near a meeting room at the Trust’s Dewsbury office. The hippo did not enter. The Trust has described this as ‘the correct decision.’