Holding(s) in Company

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARESi

1. Identity of the issuer or the underlying issuerof existing shares to which voting rights areattached: ii

Hydro International PLC

2 Reason for the notification (please tick the appropriate box or boxes):

An acquisition or disposal of voting rights

X

An acquisition or disposal of qualifying financial instruments which may result in the acquisition of shares already issued to which voting rights are attached

An acquisition or disposal of instruments with similar economic effect to qualifying financial instruments

An event changing the breakdown of voting rights

Other (please specify):

3. Full name of person(s) subject to thenotification obligation: iii

Impax Asset Management Limited

4. Full name of shareholder(s)  (if different from 3.):iv

Impax Environmental Markets plc,

Impax Environmental Markets (Ireland) Fund,

The Environmental Agency Fund

5. Date of the transaction and date onwhich the threshold is crossed orreached: v

20 October 2011

6. Date on which issuer notified:

25 October 2011

7. Threshold(s) that is/are crossed orreached: vi, vii

10%

8. Notified details:

A: Voting rights attached to shares viii, ix

Class/type ofshares

if possible usingthe ISIN CODE

Situation previousto the triggeringtransaction

Resulting situation after the triggering transaction

NumberofShares

NumberofVotingRights

Numberof shares

Number of votingrights

% of voting rights x

Direct

Direct xi

Indirect xii

Direct

Indirect

ORD

1,484,500

10.3363%

1,404,500

n/a

1,404,500

0

9.7793%

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Expirationdate xiii

Exercise/Conversion Period xiv

Number of votingrights that may beacquired if theinstrument isexercised/ converted.

% of votingrights

n/a

n/a

n/a

n/a

n/a

C: Financial Instruments with similar economic effect to Qualifying Financial Instruments xv, xvi

Resulting situation after the triggering transaction

Type of financialinstrument

Exercise price

Expiration date xvii

Exercise/Conversion period xviii

Number of voting rights instrument refers to

% of voting rights xix, xx

n/a

n/a

n/a

n/a

n/a

Nominal

Delta

Total (A+B+C)

Number of voting rights

Percentage of voting rights

1,404,500

9.7793%

9. Chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held, if applicable: xxi

Impax Environmental Markets plc - 887,100 shares = 6.1767%,

Impax Environmental Markets (Ireland) Fund - 375,000 shares = 2.6111%,

The Environmental Agency Fund - 142,400 shares = 0.9915%

Proxy Voting:

10. Name of the proxy holder:

n/a

11. Number of voting rights proxy holder will ceaseto hold:

n/a

12. Date on which proxy holder will cease to holdvoting rights:

n/a

13. Additional information:

n/a

14. Contact name:

Tony Hollox

15. Contact telephone number:

01275 878371