The Canal & River Trust had pension losses of £66.8m in 2016/17, causing its pension fund liability to more than double over the course of the year, its latest accounts show.
The charity’s accounts for the year to 31 March 2017, filed with Companies House this week, show a significant change from the pension valuation in 2015/16 when there was a gain of £36.8m.
This left the charity’s pension fund liability at £116.1m compared with £51.4m the previous year, the accounts show.
The accounts say that the pension loss is mainly due to "adverse changes to discount rate and inflation assumptions".
A spokeswoman for the charity said that lower investment returns and higher inflation were factors in the increased amount of future pension liabilities.
The charity, which was formed when British Waterways was spun out from the public sector in 2012, is part of the Waterways Pension Fund. The government promised at the time to provide the charity with more than £800m of funding over 15 years, including a one-off payment of £25m to compensate the pension deficit.
As of 30 September 2016, the defined-benefit scheme was closed to future benefit accrual.
The pension losses meant that the net movement in funds at the Canal & River Trust show a loss of £12.9m in 2016/17 compared with a £77.3m gain the previous year.
But income has increased at the charity over the past year, rising from £189.7m to £202.9m in 2016/17.
The charity made a £48.4m gain on investments compared with £37.8m the previous year, which amounts to a 28 per cent increase, according to the accounts.
Charitable expenditure was £156.9m, which was a 6 per cent increase on the previous year.
The accounts also say that the charity’s pension accumulation designated reserve – which is reserved for repaying any pension fund deficit that exists when a government guarantee expires in 2031 – had risen to £18.6m from £8.4m the previous year.
Stuart Mills, property director, was the highest earner at the charity, and received a total salary of £207,887, while the charity’s chief executive, Richard Parry, earned £194,405, the accounts show.
There was also a 12 per cent increase in volunteering with more than 540,000 hours given over the course of the year, the accounts say.