THESE days, the Thames is tamed by its Barrier. Its tides rise and fall obediently, and the floodwaters are kept at bay by that magnificent piece of engineering at Greenwich. It was not always so, and, if global warming goes on and the North Sea rises further, even the Barrier might not be able to contain it.

Meanwhile, the river is a living presence through the city: it is the reason that London is where it is, and the means of pleasure and profit for many; but it is not without its menace, and can be a fatal temptation to the despairing. So, each year, it receives the Church's blessing.

After a choral eucharist in Southwark Cathedral, the clergy and congregation process on to London Bridge, the most ancient of the Thames crossings, to meet their counterparts from St Magnus the Martyr, in the City, and join together at the point where the boundaries of the Southwark and London dioceses meet.

The prayer of blessing was said together by the Bishop at Lambeth, the Rt Revd Nigel Stock (above, right), and the former Bishop of Gibraltar in Europe, Dr Geoffrey Rowell, now an Assistant Bishop in the Chichester diocese. A cross was then thrown from the bridge into the river, as a sign of the two churches' prayer and concern for the river, for those who work on it, and for all those to whom it is important.

The ceremony was watched from the river by the crew of the RNLI lifeboat based at Tower Lifeboat Station, which was established after the inquiry into the collision between the pleasure cruiser The Marchioness and the dredger Bowbelle in 1989, when many young lives were lost. The memorial to the 51 victims is in Southwark Cathedral.