The Hogsmill in August 2019

For much of the month until the late heatwave it was more like a typical summer along the Hogsmill: cool with plenty of showers. This wasn’t good for holidays but was better for the river and its wildlife: providing more vitality for the river; and green in the meadows that led to a burst of wildflowers for insects to enjoy.

“Sweet, blue and yellow in Six Acre Meadow”

This newsletter summarises the results of River Monitoring Initiative (RMI) sampling in August; and other river-related activities that monitor and aim to restore the habitat along the Hogsmill river. These are mostly undertaken by volunteers working with the South East Rivers Trust (SERT) and local groups, and alongside the Environment Agency (EA) and local water companies, mainly Thames Water (TW).

The Hogsmill in August

We had slightly more than average rainfall between RMI “weekends” this month. This gave a boost to the river level, which for the fourth month in a row was above the lows of last year at Worcester Park.

Average Daily River Level at Worcester Park 1.6 1.5 1.4 1.3 1.2 Metres 1.1 1.0 0.9

2018 2019

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The level has also been more stable with the rain spread out and not the occasional “deluges” of the early summer; and for much of the month there has been a steady flow of water, with a few small surges after rain. The water has also generally looked clearer and less affected by algae and weed than recent summers, though a notable exception is around Middle Mill where extensive weed has blanketed the river.

Elmbridge “rapids” Middle Mill weed

Misconnected wastewater pipes and cross-connected sewers are a major source of pollution in the Hogsmill and checking outfalls is an important part of monitoring activities. Following TW work to address these problems, the visible signs of pollution are now generally much less and more sporadic than they once were.

The same has been true this month. But some have still been found. A large amount of scum appeared by the Ewell Gauging Station, rather a puzzle as there was no obvious source nearby; and the outfall by the Berrylands Railway Bridge was badly polluted later in the month, having been clear a few days earlier. This is the “horrid outfall” for August.

Ewell Gauging Station Rose Walk, Berrylands

If you see pollution along the river or indications of possible pollution, such as dying fish, please call the EA

Hotline: 0800 80 70 60; and ideally take a photo.

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Hogsmill RMI in August

The RMI is a national scheme for monitoring the health of rivers. Monthly surveys are undertaken using a standard net sampling technique to count the number of certain “water quality sensitive” invertebrates. An overall “score” is then calculated. A sharp fall or a drop below a “trigger” level could indicate pollution.

7 sites were surveyed between August 16th and 19th, some in quite challenging conditions!

“Sampling in the rain” Middle Mil “There’s weed in my bucket!”

Overall the scores were down from last month’s record, but still good for August, which has tended to be a low scoring month. Perhaps the higher water level this summer is having an impact?

Results at the individual sites varied quite noticeably across the different stretches of the river, though we don’t know why:

• At the 2 downstream sites, scores were again well above normal. There was another “9” at Berrylands; and this time counts of both olives and gammarus were substantially up to levels only once seen before here. There was an “8” at Middle Mill, which though down on July was a higher score than had been recorded in the previous 2 years; and the gammarus count was the highest ever; • Little change from July at the upstream sites by Green Lanes, where the scores were close to the long-term average and slightly above the August norm, which has tended to be a low scoring month; • Lower counts than July, particularly of gammarus, at both the mid-stream sites - Ewell Storm Tanks and Bonesgate - that resulted in a fall to a “5” at the Tanks. This raised suspicions of a possible overflow from the Tanks, but we couldn’t find any evidence of one and the scores at both sites were broadly in line with previous Augusts.

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Hogsmill RMI Scores August 2019 12.0 10.0 8.0 6.0

4.0 RMI RMI Score 2.0

0.0

Average Average Average Average Average Average Average

Jul2019 Jul2018 Jul2019 Jul2019 Jul2019 Jul2019 Jul2019 Jul2019

Aug 2018 Aug Aug 2019 Aug 2019 Aug 2018 Aug 2019 Aug 2018 Aug 2019 Aug 2018 Aug 2019 Aug 2018 Aug 2019 Aug 2018 Aug 2019 Aug GL Upstm GL Dwnstm Storm Tank Bonesgate Tol Brook Berrylands MiddleMill

Olives Caseless caddis Cased caddis Gammarus

As for individual species:

• Yet again total counts of olives and gammarus across all sites were little changed from the previous month, but there were some big changes in both directions at individual sites; • Cased caddis numbers fell sharply, but this is probably seasonal as in the previous 3 years the counts dropped dramatically in August. We did though find some lively specimens of different types of caddis who seemed keen to “come out to play”; • Another good month for fish with 10 or more being caught in the nets at several sites. Many were lively bullheads, one of which was seen “snacking on olives” in the tray, so perhaps we need to introduce a “fish-adjustment” into the scoring!

“Stone cased” “Black stick and caseless friend” “Green”

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The end of summer along the Hogsmill

A sign of approaching autumn this month is the appearance of colourful berries on the bushes and trees along the Hogsmill corridor. This looks like being a particularly good year for blackberries and sloes, and “hips and haws” and elder and rowan berries also appear plentiful. So perhaps it is time to dust of the recipe books and start picking to take advantages of the flavours many of these can provide?

Tolworth Court Farm Elmbridge Meadows Ewell Court

The end of summer has also meant that numbers of the insects, especially butterflies, that were so abundant a month or ago are now in steep decline. But as some compensation, some rarely seen critters have come out and posed near the Hogsmill this month, notably deer, brown hairstreaks and slow worms.

By Bonesgate in Chessington Tolworth Court Farm Tolworth (photo thanks to Phil)

Hopefully there will soon be another rarity to see. Water voles were common when the artist Millais was working by the Hogsmill nearly 175 years ago: one was originally featured in his Ophelia painting, but was removed when his friends didn’t know what it was! Since then numbers have declined as a result of poor watercourse management and predation, and none have been seen on the Hogsmill for 10 years.

But Citizen Zoo are leading a project to bring these special creatures back to the Hogsmill and they want volunteers to “Get inVOLEd”. More details are on: https://www.citizenzoo.org/water-voles/ Training days for volunteers are being held at the Hogsmill STW in Berrylands, including on Saturday August 31st . If you’d

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like to attend you can book on: https://www.eventbrite.co.uk/e/get-involed-water-vole-training-workshop- tickets-69176961153?aff=ebdssbdestsearch

Another date for the diary: if you’ve been involved in RMIs, Outfall Safaris or eel monitoring on the Hogsmill or other London rivers you are welcome to join ZSL’s Citizen Science Forum being held on 29th October at London Zoo. As well as reviews of these 3 programmes, there will be talks by experts including on “threats and opportunities” for our rivers. Details are on: https://www.eventbrite.co.uk/e/zsl-citizen-science-forum- 2019-tickets-66210347933

Comments on this newsletter and suggestions and contributions for future editions would be welcome.

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